Magnetic recording medium and cartridge

ABSTRACT

A magnetic recording medium is a tape-shaped magnetic recording medium, including: a substrate; an underlayer provided on the substrate; and a magnetic layer provided on the underlayer. The substrate contains polyester, each of the underlayer and the magnetic layer contains a lubricant, the magnetic layer has a surface on which a large number of holes is provided, the arithmetic average roughness Ra of the surface is 2.5 nm or less, a BET specific surface area of the entire magnetic recording medium measured in a state where the magnetic recording medium has been washed and dried is 3.5 m 2 /g or more and 7.0 m 2 /g or less, a squareness ratio of the magnetic layer in a vertical direction is 65% or more, an average thickness of the magnetic layer is 80 nm or less, an average thickness of the magnetic recording medium is 5.6 μm or less, and a servo pattern is recorded on the magnetic layer and a statistical value δ SW  indicating a non-linearity of the servo pattern is 24 nm or less.

TECHNICAL FIELD

The present disclosure relates to a magnetic recording medium and acartridge.

BACKGROUND ART

For storage of electronic data, a tape-shaped magnetic recording mediumis widely used. In this magnetic recording medium, various types ofimprovement in characteristics have been studied.

Patent Literature 1 describes that a Root mean square surface roughness(Rq) of the surface of a magnetic layer forming surface is set to 4.0 nmor less and a skewness (Sk) in the surface profile of the magnetic layerforming surface is set to −1 or more and +1 or less in order to achieveboth excellent travelling stability and excellent electromagneticconversion characteristics.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-open No.2006-65953

DISCLOSURE OF INVENTION Technical Problem

A tape-shaped magnetic recording medium is usually housed in a cartridgecase. In order to further increase the recording capacity of acartridge, it is conceivable to increase the tape length of thecartridge by making the magnetic recording medium housed in thecartridge thinner (by reducing the total thickness). However, a magneticrecording medium having a small total thickness has poor travellingstability in some cases. In particular, in the case of repeatedlyperforming recording and/or reproduction, the surface state,particularly, the surface state relating to friction, of the magneticrecording medium having a small total thickness changes, and thetravelling stability deteriorates in some cases.

It is an object of the present disclosure to provide a magneticrecording medium and a cartridge that are capable of achieving bothexcellent travelling stability and excellent electromagnetic conversioncharacteristics even in the case where the total thickness of themagnetic recording medium is small.

Solution to Problem

In order to achieved the above-mentioned object, a first disclosure is atape-shaped magnetic recording medium, including: a substrate; anunderlayer provided on the substrate; and a magnetic layer provided onthe underlayer, in which the substrate contains polyester, each of theunderlayer and the magnetic layer contains a lubricant, the magneticlayer has a surface on which a large number of holes is provided, thearithmetic average roughness Ra of the surface is 2.5 nm or less, a BETspecific surface area of the entire magnetic recording medium measuredin a state where the magnetic recording medium has been washed and driedis 3.5 m²/g or more and 7.0 m²/g or less, a squareness ratio of themagnetic layer in a vertical direction is 65% or more, an averagethickness of the magnetic layer is 80 nm or less, an average thicknessof the magnetic recording medium is 5.6 μm or less, and a servo patternis recorded on the magnetic layer and a statistical value σ_(SW)indicating a non-linearity of the servo pattern is 24 nm or less.

A second disclosure is a cartridge, including: the magnetic recordingmedium according to the first disclosure; and a storage unit that has aregion to which adjustment information for adjusting tension to beapplied in a longitudinal direction of the magnetic recording medium iswritten.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing an example of a configuration of arecording/reproduction system according to a first embodiment of thepresent disclosure.

FIG. 2 is an exploded perspective view showing an example of aconfiguration of a cartridge.

FIG. 3 is a block diagram showing an example of a configuration of acartridge memory.

FIG. 4 is a cross-sectional view showing an example of a configurationof a magnetic tape.

FIG. 5 is a schematic diagram showing an example of the layout of databands and servo bands.

FIG. 6 is an enlarged view showing an example of a configuration of thedata bands.

FIG. 7 is an enlarged view showing an example of the configuration ofthe servo bands.

FIG. 8 is a schematic diagram of a head unit used in measuring astatistical value σ_(SW).

FIG. 9 Part A and Part B of FIG. 9 are each a diagram showing an exampleof a TEM photograph of a magnetic layer.

FIG. 10 Part A and Part B of FIG. 10 are each a schematic diagramdescribing a method of measuring a friction coefficient between amagnetic surface and the magnetic head.

FIG. 11 is a schematic diagram showing an example of a configuration ofa servo writer.

FIG. 12 Part A of FIG. 12 is a perspective view showing an example of aconfiguration of a servo signal writing head. Part B of FIG. 12 is across-sectional view taken along the line XIIB-XIIB in Part A of FIG. 12.

FIG. 13 is a flowchart describing an example of an operation of arecording/reproduction apparatus during data recording.

FIG. 14 is a flowchart describing an example of the operation of therecording/reproduction apparatus during data reproduction.

FIG. 15 is a schematic diagram showing an example of a configuration ofa recording/reproduction system according to a second embodiment of thepresent disclosure.

FIG. 16 is a flowchart describing an example of an operation of therecording/reproduction apparatus during data recording.

FIG. 17 is flowchart describing an example of the operation of therecording/reproduction apparatus during data reproduction.

MODE(S) FOR CARRYING OUT THE INVENTION

Embodiments of the present disclosure will be described in the followingorder.

Note that the same or corresponding components will be denoted by thesame reference symbols in all the figures of the following embodiments.

1 First Embodiment

2 Second Embodiment

3 Modified Example

1 First Embodiment

[Configuration of Recording/Reproduction System]

FIG. 1 is a schematic diagram showing an example of a configuration of arecording/reproduction system 100 according to a first embodiment of thepresent disclosure. The recording/reproduction system 100 is a magnetictape recording/reproduction system, and includes a cartridge 10, and arecording/reproduction apparatus 50 configured to be capable of loadingand unloading the cartridge 10.

[Configuration of Cartridge]

FIG. 2 is an exploded perspective view showing an example of aconfiguration of the cartridge 10. The cartridge 10 is a magnetic tapecartridge conforming to the LTO (Linear Tape-Open) standard, andincludes, inside a cartridge case 12 including a lower shell 12A and anupper shell 12B, a reel 13 in which a magnetic tape (tape-shapedmagnetic recording medium) MT is wound, a reel lock 14 and a reel spring15 for locking rotation of the reel 13, a spider 16 for releasing thelock state of the reel 13, a sliding door 17 that opens and closes atape outlet 12C provided across the lower shell 12A and the upper shell12B in the cartridge case 12, a door spring 18 that urges the slidingdoor 17 to the closed position of the tape outlet 12C, a write protect19 for preventing accidental erasure, and a cartridge memory 11. Thereel 13 has a substantially disc shape having an opening at the centerportion, and includes a reel hub 13A and a flange 13B formed of a hardmaterial such as plastic. A leader pin 20 is provided to one end portionof the magnetic tape MT.

The cartridge memory 11 is provided in the vicinity of one cornerportion of the cartridge 10. In the state where the cartridge 10 isloaded on the recording/reproduction apparatus 50, the cartridge memory11 faces a reader/writer 57 of the recording/reproduction apparatus 50.The cartridge memory 11 communicates with the recording/reproductionapparatus 50, specifically, the reader/writer 57, with a wirelesscommunication standard conforming to the LTO standard.

[Configuration of Cartridge Memory]

FIG. 3 is a block diagram showing an example of a configuration of thecartridge memory 11. The cartridge memory 11 includes an antenna coil(communication unit) 31, that performs communication with thereader/writer 57 with a specified communication standard, arectification/power circuit 32 that generates power using an induceelectromotive force from the radio wave received by the antenna coil 31and rectifies the power to generate a power source, a clock circuit 33that generates a clock from the radio wave received by the antenna coil31 by using the an induce electromotive force similarly, adetection/modulation circuit 34 that detects the radio wave received bythe antenna coil 31 and modulates a signal transmitted by the antennacoil 31, a controller (control unit) 35 that includes a logic circuit orthe like for discriminating and processing commands and data from thedigital signal extracted from the detection/modulation circuit 34, and amemory (storage unit) 36 that stores information. Further, the cartridgememory 11 includes a capacitor 37 connected to the antenna coil 31 inparallel, and the antenna coil 31 and the capacitor 37 constitute aresonance circuit.

The memory 36 stores information relating to the cartridge 10, and thelike. The memory 36 is a non-volatile memory (NVM). The storage capacityof the memory 36 is favorably approximately 32 KB or more.

The memory 36 includes a first storage region 36A and a second storageregion 36B. The first storage region 36A corresponds to the storageregion of a cartridge memory (hereinafter, referred to as “existingcartridge memory”) of the LTO standard before LTO8, and is a region forstoring information conforming to the LTO standard before LTO8. Examplesof the information conforming to the LTO standard before LTO8 includeproduction information (e.g., a unique number for the cartridge 10) anda usage history (e.g., number of tape withdrawals (Thread Count)).

The second storage region 36B corresponds to the extended storage regionfor the storage region of the existing cartridge memory. The secondstorage region 36B is a region for storing additional information. Here,the additional information means information relating to the cartridge10, which is not defined in the LTO standard before LTO8. Examples ofthe additional information include tension adjustment information,management ledger data, Index information, and thumbnail informationregarding video stored in the magnetic tape MT, but the presentdisclosure is not limited to these types of data. The tension adjustmentinformation is information for adjusting tension to be applied to themagnetic tape MT in the longitudinal direction. The tension adjustmentinformation includes a distance between adjacent servo bands (distancebetween servo patterns recorded in adjacent servo bands) during datarecording in the magnetic tape MT. The distance between adjacent servobands is an example of width-related information relating to the widthof the magnetic tape MT. Details of the distance between servo bandswill be described below. In the following description, information to bestored in the first storage region 36A will be referred to as “firstinformation” and information to be stored in the second storage region36B will be referred to as “second information” in some cases.

The memory 36 may include a plurality of banks. In this case, a part ofthe plurality of banks may constitute the first storage region 36A, andthe other banks may constitute the second storage region 36B.

The antenna coil 31 induces an induced voltage by electromagneticinduction. The controller 35 communicates with therecording/reproduction apparatus 50 via the antenna coil 31 with aspecified communication standard. Specifically, for example, thecontroller 35 performs mutual authentication, commandtransmission/reception, or data exchange.

The controller 35 stores, in the memory 36, information received fromthe recording/reproduction apparatus 50 via the antenna coil 31. Forexample, the tension adjustment information received from therecording/reproduction apparatus 50 via the antenna coil 31 is stored inthe second storage region 36B of the memory 36. In response to a requestfrom the recording/reproduction apparatus 50, the controller 35 readsinformation from the memory 36 and transmits the information to therecording/reproduction apparatus 50 via the antenna coil 31. Forexample, in response to a request from the recording/reproductionapparatus 50, the controller 35 reads tension adjustment informationfrom the second storage region 36B of the memory 36 and transmits thetension adjustment information to the recording/reproduction apparatus50 via the antenna coil 31.

[Configuration of Magnetic Tape]

FIG. 4 is a cross-sectional view showing an example of a configurationof the magnetic tape MT. The magnetic tape MT is a tape-shaped magneticrecording medium, and includes an elongated substrate 41, an underlayer42 provided on one main surface (first main surface) of the substrate41, a magnetic layer 43 provided on the underlayer 42, and a back layer44 provided on the other main surface (second main surface) of thesubstrate 41. Note that the underlayer 42 and the back layer 44 areprovided as necessary, and do not necessarily need to be provided. Themagnetic tape MT may be a perpendicular recording type magneticrecording medium or a longitudinal recording type magnetic recordingmedium.

The magnetic tape MT has a long tape shape, and is caused to travel inthe longitudinal direction at the time of recording/reproduction. Notethat the surface of the magnetic layer 43 is a surface on which amagnetic head 56 of the recording/reproduction apparatus 50 is caused totravel. The magnetic tape MT is favorably used in arecording/reproduction apparatus including a ring-type head as arecording head. The magnetic tape MT is favorably used in arecording/reproduction apparatus configured to be capable of recordingdata with a data track width of 1500 nm or less or 1000 nm or less.

(Substrate)

The substrate 41 is a non-magnetic support that supports the underlayer42 and the magnetic layer 43. The substrate 41 has a long film shape.The upper limit value of the average thickness of the substrate 41 isfavorably 4.2 μm or less, more favorably 3.8 μm or less, and still morefavorably 3.4 μm or less. In the case where the upper limit value of theaverage thickness of the substrate 41 is 4.2 μm or less, the recordingcapacity of one data cartridge can be increased as compared with that ofa general magnetic tape. The lower limit value of the average thicknessof the substrate 41 is favorably 3 μm or more, more favorably 3.2 μm ormore. In the case where the lower limit value of the average thicknessof the substrate 41 is 3 μm or more, the reduction in strength of thesubstrate 41 can be suppressed.

The average thickness of the substrate 41 is obtained as follows. First,the magnetic tape MT having a width of ½ inch is prepared and cut into a250 mm length to prepare a sample. Subsequently, layers (i.e., theunderlayer 42, the magnetic layer 43, and the back layer 44) of thesample other than the substrate 41 are removed with a solvent such asMEK (methyl ethyl ketone) and dilute hydrochloric acid. Next, thethickness of the sample (substrate 41) is measured at five or morepoints by using a laser hologauge (LGH-110C) manufactured by MitsutoyoCorporation as a measurement apparatus, and the measured values aresimply averaged (arithmetic average) to calculate the average thicknessof the substrate 41. Note that the measurement positions are randomlyselected from the sample.

The substrate 41 contains polyester. Since the substrate 41 includespolyester, it is possible to reduce the Young's modulus of the substrate41 in the longitudinal direction. Therefore, it is possible to keep thewidth of the magnetic tape MT constant or substantially constant byadjusting, by the recording/reproduction apparatus 50, the tension ofthe magnetic tape MT in the longitudinal direction during travelling.

The polyester includes, for example, at least one of polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), polybutyleneterephthalate (PBT), polybutylene naphthalate (PBN),polycyclohexylenedimethylene terephthalate (PCT),polyethylene-p-oxybenzoate (PEB), or polyethylene bisphenoxycarboxylate. In the case where the substrate 41 contains two or moretypes of polyesters, the two or more types of polyesters may be mixed,copolymerized, or stacked. At least one of the terminal and side chainsof polyester may be modified.

It is confirmed, for example, as follows, that the substrate 41 containspolyester. First, the layers of the sample other than the substrate 41are removed in a similar way as the method of measuring the averagethickness of the substrate 41. Next, the IR spectrum of the sample(substrate 41) is obtained by infrared absorption spectrometry (IR). Onthe basis of this IR spectrum, it can be confirmed that the substrate 41contains polyester.

The substrate 41 may further contain, for example, at least one type ofpolyamide, polyimide, and polyamideimide in addition to polyester, ormay further contain at least one type of polyamide, polyimide,polyamideimide, polyolefins, cellulose derivatives, vinyl resins, andother polymer resins. Polyamide may be aromatic polyamide (aramid).Polyimide may be aromatic polyimide. Polyamideimide may be aromaticpolyamideimide.

In the case where the substrate 41 contains a polymer resin other thanpolyesters, it is favorable that the substrate 41 contains polyester asa main component. Here, the main component means the component with thelargest content (mass ratio) among polymer resins contained in thesubstrate 41. In the case where the substrate 41 contains a polymerresin other than polyesters, polyester and a polymer resin other thanpolyester may be mixed or copolymerized.

The substrate 41 may be biaxially stretched in the longitudinaldirection and the width direction. It is favorable that the polymerresin contained in the substrate 41 is oriented in an oblique directionwith respect to the width direction of the substrate 41.

(Magnetic Layer)

The magnetic layer 43 is a recording layer for recording a signal with amagnetization pattern. The magnetic layer 43 may be perpendicularrecording type recording layer, or a longitudinal recording typerecording layer. The magnetic layer 43 contains, for example, a magneticpowder, a binder, and a lubricant. The magnetic layer 43 may furthercontain, as necessary, at least one additive of an antistatic agent, anabrasive, a curing agent, a rust inhibitor, a non-magnetic reinforcingparticle, and the like.

The magnetic layer 43 has a surface on which a large number of holes 43Ais provided. These holes 43A each store a lubricant. It is favorablethat the holes 43A extend in the direction perpendicular to the surfaceof the magnetic layer 43. This is because supply of the lubricant to thesurface of the magnetic layer 43 can be improved. Note that a part ofthe holes 43A may extend in the perpendicular direction.

An arithmetic average roughness Ra of the surface of the magnetic layer43 is 2.5 nm or less, favorably 2.2 nm or less, and more favorably 1.9nm or less. In the case where the arithmetic average roughness Ra is 2.5nm or less, output reduction due to spacing loss can be suppressed, andthus, excellent electromagnetic conversion characteristics can beachieved. The lower limit value of the arithmetic average roughness Raof the surface of the magnetic layer 43 is favorably 1.0 nm or more,more favorably 1.2 nm or more, and still more favorably 1.4 nm or more.In the case where the lower limit value of the arithmetic averageroughness Ra of the surface of the magnetic layer 43 is 1.0 nm or more,it is possible to suppress reduction in traveling due to an increase infriction.

The arithmetic average roughness Ra is obtained as follows. First, thesurface of the magnetic layer 43 is observed with an AFM (Atomic ForceMicroscope) to obtain an AFM image of 40 μm×40 μm. Nano Scope IIIa D3100manufactured by Digital Instruments is used as an AFM, a cantileverformed of silicon single crystal is used (Note 1), and measurement isperformed with 200 to 400 Hz tuning as tapping frequency. Next, the AFMimage is divided into 512×512 (=262,144) measurement points, heightsZ(i) (i: measurement point number, i=1 to 262,144) are measured at themeasurement points, and the measured heights Z(i) at the measurementpoints are simply averaged (arithmetic average) to obtain an averageheight (average surface) Zave (=Z(1)+Z(2)+ . . . +Z(262,144))/262,144).Subsequently, deviations Z″(i)(=Z(i)−Zave) from the average center lineat the measurement points are obtained, and the arithmetic averageroughness Ra[nm](=(Z″(1)+Z″(2)+ . . . +Z″(262,144))/262,144) iscalculated. At this time, one on which filtering processing has beenperformed by Flatten order 2 and planefit order 3 XY as image processingis used as data.

(Note 1) SPM probe NCH normal type PointProbe L (cantilever length)=125manufactured by Nano World

The lower limit value of the BET specific surface area of the entiremagnetic tape MT measured in the state where the magnetic tape MT hasbeen washed and dried is 3.5 m²/g or more, favorably 4 m²/g or more,more favorably 4.5 m²/g or more, and still more favorably 5 m²/g ormore. In the case where the lower limit value of the BET specificsurface area is 3.5 m²/g or more, it is possible to suppress thedecrease in the amount of lubricant supplied between the surface of themagnetic layer 43 and the magnetic head 56 even after recording orreproduction is repeatedly performed (i.e., even after the magnetic tapeMT is caused to repeatedly travel while the magnetic head 56 is incontact with the surface of the magnetic tape MT). Therefore, it ispossible to suppress the increase in the dynamic friction coefficient.Therefore, excellent travelling stability can be achieved.

The upper limit value of the BET specific surface area of the entiremagnetic tape MT measured in the state where the magnetic tape MT hasbeen washed and dried is 7 m²/g or less, favorably 6 m²/g or less, andmore favorably 5.5 m²/g or less. In the case where the upper limit valueof the BET specific surface area is 7 m²/g or less, it is possible tosufficiently supply a lubricant without depletion even after travellingis performed many times. Therefore, it is possible to suppress theincrease in the dynamic friction coefficient. Therefore, excellenttravelling stability can be achieved.

The average pore diameter of the entire magnetic tape MT measured in thestate where the magnetic tape MT has been washed and dried is 6 nm ormore and 11 nm or less, favorably 7 nm or more and 10 nm or less, andmore favorably 7.5 nm or more and 10 nm or less. In the case where theaverage pore diameter is 6 nm or more and 11 nm or less, it is possibleto further improve the effect of suppressing the increase in theabove-mentioned dynamic friction coefficient. Therefore, furtherexcellent travelling stability can be obtained.

The BET specific surface area and the pore distribution (the pore volumeand the average pore diameter (pore diameter of the maximum pore volumeat the time of attachment/detachment)) of the entire magnetic tape MTmeasured in the state where the magnetic tape MT has been washed anddried are obtained as follows. First, the magnetic tape MT having a sizeapproximately 10% larger than the area 0.1265 m² is soaked in hexane(with the amount that the magnetic tape MT can be sufficiently immersed,for example, 150 mL) for 24 hours, and then is naturally dried and cutout to a size of the area 0.1265 m² (for example, both ends of the driedmagnetic tape MT are cut off by 50 cm to prepare a tape width×10 m) toprepare a measurement sample. Next, the BET specific surface area isobtained using a specific surface area/pore distribution measurementapparatus. Further, the pore distribution (the pore volume and theaverage pore diameter) is obtained by a BJH method using the specificsurface area/pore distribution measurement apparatus. The measurementapparatus and measurement conditions are shown in the following. In thisway, the average diameter of the pores is measured.

Measurement environment: room temperature

Measurement apparatus:3FLEX manufactured by Micromeritics InstrumentCorp.

Measurement adsorbate: N₂ gas

Measured pressure range (P/P₀ (relative pressure)): 0 to 0.995

Regarding the measured pressure range, the pressure is changed as shownin the following Table 1. The pressure values in the following Table 1are each a relative pressure P/P₀. For example, in Step 1 in thefollowing Table 1, the pressure is changed from the starting pressure0.000 to the ultimate pressure 0.010 by 0.001 per 10 seconds. When thepressure reaches the ultimate pressure, the pressure change in the nextStep is performed. The same applies to Steps 2 to 10. However, in thecase where the pressure does not reach equilibrium in each Step, theprocessing proceeds to next Step after the apparatus stands by until thepressure to equilibrate.

TABLE 1 Starting Pressure Ultimate pressure change step pressure 1 0.0000.001/10 sec  0.010 2 0.010 0.02/10 sec 0.100 3 0.100 0.05/10 sec 0.6004 0.600 0.05/10 sec 0.950 5 0.950 0.05/10 sec 0.990 6 0.990 0.05/10 sec0.995 7 0.995 0.01/10 sec 0.990 8 0.990 0.01/10 sec 0.950 9 0.9500.05/10 sec 0.600 10 0.600 0.05/10 sec 0.300

As shown in FIG. 5 , the magnetic layer 43 includes a plurality of servobands SB and a plurality of data bands DB in advance. The plurality ofservo bands SB is provided in the width direction of the magnetic tapeMT at equal intervals. Between adjacent servo bands SB, a data band DBis provided. The servo band SB is for guiding the magnetic head 56(specifically, servo lead heads 56A and 56B) at the time of recording orreproducing data. In each of the servo bands SB, a servo pattern (servosignal) for tracking controlling of the magnetic head 56 is written inadvance. In each of the data bands DB, user data is recorded.

The upper limit value of a ratio R_(S) (=(S_(SB)/S)×100) of a total areaS_(SB) of the servo bands SB to an area S of the surface of the magneticlayer 43 is favorably 4.0% or less, more favorably 3.0% or less, andstill more favorably 2.0% or less from the viewpoint of securing a highrecording capacity. Meanwhile, the lower limit value of the ratio R_(S)of the total area S_(SB) of the servo bands SB to the area S of thesurface of the magnetic layer 43 is favorably 0.8% or more from theviewpoint of securing five or more servo bands SB.

The ratio R_(S) of the total area S_(SB) of the servo bands SB to thearea S of the entire surface of the magnetic layer 43 is obtained asfollows. The magnetic tape MT is developed using a ferricolloiddeveloper (manufactured by SIGMA HI-CHEMICAL INC., SigMarker Q). Afterthat, the developed magnetic tape MT is observed with an opticalmicroscope, and a servo band width W_(SB) and the number of servo bandsSB are measured. Next, the ratio R_(S) is obtained on the basis of thefollowing formula.Ratio R _(S)[%]=(((servo band width W _(SB))×(number of servo bandsSB))/(width of the magnetic tapeMT))×100

The number of servo bands SB is favorably five or more, more favorably5+4n (where n represents a positive number). In the case where thenumber of servo bands SB is five or more, the influence on the servosignal due to the dimensional change of the magnetic tape MT in thewidth direction is suppressed, and stable recording/reproductioncharacteristics with less off-track can be secured. Although the upperlimit value of the number of servo bands SB is not particularly limited,it is, for example, 33 or less.

The number of servo bands SB is obtained in a similar way as theabove-mentioned method of calculating the ratio R_(S).

The upper limit value of the servo band width W_(SB) is favorably 95 μmor less, more favorably 60 μm or less, and still more favorably 30 μm orless from the viewpoint of securing a high recording capacity. The lowerlimit value of the servo band width W_(SB) is favorably 10 μm or more.It is difficult to produce the recording head 56 capable of reading aservo signal of the servo band width W_(SB) of less than 10 μm.

The width of the servo band width W_(SB) is obtained in a similar way asthe above-mentioned method of calculating the ratio R_(S).

As shown in FIG. 6 , the magnetic layer 43 is configured to be capableof forming a plurality of data tracks Tk in the data band DB. The upperlimit value of a data track width W is favorably 2000 nm or less, morefavorably 1500 nm or less, and still more favorably 1000 nm or less fromthe viewpoint of improving the track recording density and securing ahigh recording capacity. The lower limit value of the data track width Wis favorably 20 nm or more considering the size of the magneticparticle.

The magnetic layer 43 is configured to be capable of recording data sothat the minimum value L of a magnetization reversal pitch is favorably48 nm or less, more favorably 44 nm or less, and still more favorably 40nm or less from the viewpoint of securing a high recording capacity. Thelower limit value of the minimum value L of the magnetization reversalpitch is favorably 20 nm or more considering the size of the magneticparticle.

The magnetic layer 43 is configured to be capable of recording data sothat the minimum value L of the magnetization reversal pitch and thedata track width W satisfy the relationship of favorably W/L≤35, morefavorably W/L≤30, and still more favorably W/L≤25. If the minimum valueL of the magnetization reversal pitch is a constant value and theminimum value L of the magnetization reversal pitch and the track widthW satisfy the relationship of W/L>35 (i.e., if the track width W islarge), there is possibility that the recording capacity cannot besufficiently secured because the track recording density does notincrease. Further, if the track width W is a constant value and theminimum value L of the magnetization reversal pitch and the track widthW satisfy the relationship of W/L>35 (i.e., if the minimum value L ofthe magnetization reversal pitch is small), there is a possibility thatthe electromagnetic conversion characteristics (e.g., SNR(Signal-to-Noise Ratio)) deteriorate due to the influence of spacingloss although the bit length is reduced and the linear recording densityincreases. Therefore, in order to suppress the deterioration of theelectromagnetic conversion characteristics (e.g., SNR) while securingthe recording capacity, it is favorable that W/L is within the range of35 or less (W/L≤35) as described above. The lower limit value of W/L isnot particularly limited, and may be, for example, 1≤W/L.

The data track width W is obtained as follows. The magnetic tape MT withdata recorded on the entire surface thereof is prepared, and a datarecording pattern of the data band DB part of the magnetic layer 43 isobserved using a magnetic force microscope (MFM) to obtain an MFM image.As the MFM, Dimension 3100 manufactured by Digital Instruments and theanalysis software thereof are used. The measurement region of the MFMimage has a size of 10 μm×10 μm, and the measurement region having thesize of 10 μm×10 μm is divided into 512×512 (=262,144) measurementpoints. Three measurement regions of 10 μm×10 μm at different locationsare measured with the MFM, i.e., three MFM images are obtained. From thethree obtained MFM images, track widths are measured at 10 locationsusing the analysis software attached to Dimension 3100, and the averagevalue (simple average) thereof is obtained. The average value is thedata track width W. Note that the measurement conditions of theabove-mentioned MFM are sweep speed: 1 Hz, used chip: MFMR-20, liftheight: 20 nm, and correction: Flatten order 3.

The minimum value L of the magnetization reversal pitch is obtained asfollows. The magnetic tape MT with data recorded on the entire surfacethereof is prepared, and a data recording pattern of the data band DBpart of the magnetic layer 43 is observed using a magnetic forcemicroscope (MFM) to obtain an MFM image. As the MFM, Dimension 3100manufactured by Digital Instruments and the analysis software thereofare used. The measurement region of the MFM image has a size of 2 μm×2μm, and the measurement region having the size of 2 μm×2 μm is dividedinto 512×512 (=262,144) measurement points. Three measurement regions of2 μm×2 μm at different locations are measured with the MFM, i.e., threeMFM images are obtained. Fifty distances between bits are measured fromthe two-dimensional unevenness chart of the recording pattern of theobtained MFM image. The distance between bits is measured using theanalysis soft attached to Dimension 3100. The value that issubstantially the greatest common divisor of the 50 measured distancesbetween bits is taken as the minimum value of the magnetization reversalpitch L. Note that the measurement conditions of the above-mentioned MFMare sweep speed: 1 Hz, used chip: MFMR-20, lift height: 20 nm, andcorrection: Flatten order 3.

The servo pattern is a magnetized region, and is formed by magnetizing aspecific region of the magnetic layer 43 in a specific direction with aservo write head during production of the magnetic tape. Of the servoband SB, a region in which no servo pattern is formed (hereinafter,referred to as “non-pattern region”) may be a magnetized region in whichthe magnetic layer 43 has been magnetized or a non-magnetized region inwhich the magnetic layer 43 has not been magnetized. In the case wherethe non-pattern region is a magnetized region, the servo pattern formingregion and the non-pattern region have been magnetized in differentdirections (e.g., opposite directions).

In the LTO standard, as shown in FIG. 7 , servo patterns including aplurality of servo stripes (linear magnetized regions) 113 inclined withrespect to the width direction of the magnetic tape MT are formed in theservo band SB.

The servo band SB includes a plurality of servo frames 110. Each of theservo frames 110 includes 18 servo stripes 113. Specifically, each ofthe servo frames 110 includes a servo subframe 1 (111) and a servosubframe 2 (112).

The servo subframe 1 (111) includes an A burst 111A and a B burst 111B.The B burst 111B is disposed adjacent to the A burst 111A. The A burst111A includes five servo stripes 113 that are inclined with respect tothe width direction of the magnetic tape MT at a predetermined angle φand formed apart by specified intervals. In FIG. 7 , the five servostripes 113 are denoted by reference symbols A₁, A₂, A₃, A₄, and A₅ fromthe EOT (End Of Tape) to BOT (Beginning Of Tape) of the magnetic tapeMT. Similarly to the A burst 111A, the B burst 111B includes five servostripes 113 that are inclined with respect to the width direction of themagnetic tape MT at the predetermined angle φ and formed apart byspecified intervals. In FIG. 7 , the five servo stripes 113 are denotedby reference symbols B₁, B₂, B₃, B₄, and B₅ from the EOT to BOT of themagnetic tape MT. The servo stripes 113 of the B burst 111B are inclinedin the opposite direction to the servo stripes 113 of the A burst 111A.That is, the servo stripes 113 of the A burst 111A and the servo stripes113 of the B burst 111B are arranged in the inverted V shape.

The servo subframe 2 (112) includes a C burst 112C and a D burst 112D.The D burst 112D is disposed adjacent to the C burst 112C. The C burst112C includes four servo stripes 113 that are inclined with respect tothe tape width direction at the predetermined angle φ and formed apartby specified intervals. In FIG. 7 , the four servo stripes 113 aredenoted by reference symbols C₁, C₂, C₃, and C₄ from the EOT to BOT ofthe magnetic tape MT. Similarly to the C burst 112C, the D burst 112Dincludes four servo stripes 113 that are inclined with respect to thetape width direction at the predetermined angle φ and formed apart byspecified intervals. In FIG. 7 , the four servo stripes 113 are denotedby reference symbols D₁, D₂, D₃, and D₄ from the EOT to BOT of themagnetic tape MT. The servo stripes 113 of the D burst 112D are inclinedin the opposite direction to the servo stripes 113 of the C burst 112C.That is, the servo stripes 113 of the C burst 112C and the servo stripes113 of the D burst 112D are arranged in the inverted V shape.

The above-mentioned predetermined angle φ of the servo stripes 113 inthe A burst 111A, the B burst 111B, the C burst 112C, and the D burst112D is, for example, 5° or more and 25° or less, and can beparticularly 11° or more and 25° or less.

By reading the servo band SB with the magnetic head 56, information forobtaining the tape speed and the position of the magnetic head in thelongitudinal direction can be acquired. The tape speed is calculated onthe basis of the time between four timing signals (A1-C1, A2-C2, A3-C3,and A4-C4). The head position is calculated on the basis of theabove-mentioned time between four timing signals and the time betweenother four timing signals (A1-B1, A2-B2, A3-B3, and A4-B4).

As shown in FIG. 7 , it is favorable that the servo patterns (i.e., theplurality of servo stripes 113) are linearly arranged toward thelongitudinal direction of the magnetic tape MT. That is, it is favorablethat the servo band SB has a straight line shape in the longitudinaldirection.

The statistical value σ_(SW) indicating the non-linearity of arrangementof the servo patterns (non-linearity of the servo band SB) is 24 nm orless, favorably 23 nm or less, more favorably 20 nm or less, and stillmore favorably 15 nm or less. In the case where the statistical valueσ_(SW) is 24 nm or less, it is possible to prevent the servo patternsfrom swinging in the width direction of the magnetic tape MT. That is,it is possible to achieve arrangement of the servo patterns (servo bandSB) having excellent linearity. For this reason, since the magnetic head56 can be appropriately guided by the servo patterns (servo band SB) tothe position on the magnetic tape MT where data is written, excellenttravelling stability can be achieved. Therefore, it is possible tosuppress occurrence of errors during data reading.

The statistical value σ_(SW) indicating the non-linearity of the servopatterns (non-linearity of the servo band SB) is favorably as small aspossible and is, for example, 0 or more from the viewpoint of improvingthe travelling stability.

The statistical value σ_(SW) indicating the non-linearity of the servoband is measured using a tape travelling apparatus (Tape Transportation(Mountain Engineering II, Inc.)) including a magnetic head for readingthe servo patterns recorded on the surface of the magnetic layer 43 ofthe magnetic tape MT. The magnetic head may be one that is employed in acommercially available LTO8 full height drive. The magnetic head is usedin a state being fixed to the tape travelling apparatus.

Using the tape travelling apparatus, the magnetic tape MT is caused totravel at 2 m/s so that the surface on the side of the magnetic layer 43slides on the surface of the magnetic head. Using the reading element onthe surface of the magnetic head, the reproduction waveform of the servosignal is read from the servo patterns of the magnetic tape MT using adigital oscilloscope. That is, magnetic servo patterns are convertedinto an electrical servo signal. In order to acquire the reproductionwaveform of the servo signal with sufficient accuracy, the sampling rateof the digital oscilloscope is 20,000,000 or more per second.

In order to read the servo patterns recorded in one servo band, tworeading elements arranged side by side in the longitudinal direction ofthe magnetic tape MT are used. The two reading elements are included inthe magnetic head unit adopted in an LTO8 full height drive. The tworeading elements will be described below with reference to FIG. 8 .

FIG. 8 is a schematic diagram of the magnetic head unit. A head unit 300shown in FIG. 8 includes three head units 300A, 300B, and 300C arrangedside by side along the longitudinal direction of the magnetic tape MT.The head unit 300A includes two servo heads 320A1 and 320A2 and aplurality of recording heads 340. Ellipsis-like points in the head unit300A means that the recording heads 340 are arranged. The head unit 300Bincludes two servo heads 320B1 and 320B2 and a plurality of reproductionheads 350. Ellipsis-like points in the head unit 300B means that thereproduction heads 350 are arranged. The head unit 300C includes twoservo heads 320C1 and 320C2 and a plurality of recording heads 340.Ellipsis-like points in the head unit 300C means that the recordingheads 340 are arranged.

The above-mentioned two reading elements used for acquiring theabove-mentioned statistical value σ_(SW) are only the servo head 320A1included in the head unit 300A and the servo head 320B1 included in thehead unit 300B. Other servo heads are not used therefor. Hereinafter, ofthe two reading elements, a reading element (servo head 320A1) on theunwinding side will be referred to also as the reading element a and areading element (servo head 320B1) on the winding side will be referredto also as a reading element b.

The reproduction waveform of the servo signal acquired by each readingelement is acquired by a digital oscilloscope or the like. On the basisof the acquired reproduction waveform of the servo signal, “a relativedifference p between the center line of the servo pattern and the actualpassing position of the reading element on the servo pattern” iscalculated. Specifically, the relative difference p is calculated usingthe shape of the acquired reproduction waveform of the servo signal andthe shape of the servo pattern itself.

The relative difference p is calculated by the following calculationformula.

$\begin{matrix}{{{Relative}\mspace{14mu}{difference}\mspace{14mu}{p\mspace{11mu}\lbrack{\mu m}\rbrack}} = \frac{{X\lbrack{\mu m}\rbrack} - {\left\lbrack \frac{\begin{matrix}{\left( {B_{a1} - A_{a1}} \right) + \left( {B_{a2} - A_{a2}} \right) + \left( {B_{a3} - A_{a3}} \right) + \left( {B_{a4} - A_{a4}} \right) +} \\{\left( {D_{a\; 1} - C_{a\; 1}} \right) + \left( {D_{a\; 2} - C_{a\; 2}} \right) + \left( {D_{a\; 3} - C_{a\; 3}} \right) + \left( {D_{a\; 4} - C_{a\; 4}} \right)}\end{matrix}}{\begin{matrix}{\left( {C_{a\; 1} - A_{a\; 1}} \right) + \left( {C_{a\; 2} - A_{a\; 2}} \right) + \left( {C_{a\; 3} - A_{a3}} \right) + \left( {C_{a\; 4} - A_{a4}} \right) +} \\{\left( {A_{a\; 1}^{\prime} - C_{a\; 1}} \right) + \left( {A_{a\; 2}^{\prime} - C_{a\; 2}} \right) + \left( {A_{a\; 3}^{\prime} - C_{a\; 3}} \right) + \left( {A_{a\; 4}^{\prime} - C_{a\; 4}} \right)}\end{matrix}} \right\rbrack \times {Y\left\lbrack {\mu m} \right\rbrack}}}{2 \times \tan\;\varphi}} & \left\lbrack {{Math}.\mspace{14mu} 1} \right\rbrack\end{matrix}$

The above-mentioned calculation formula of the relative difference pwill be described below with reference to FIG. 7 . The above-mentioneddifference (B_(a1)-A_(a1)) in the above-mentioned calculation formula isa difference [sec] between the time when the stripe B₁ is read by thereading element a and the time when the stripe A₁ is read by the readingelement a, and is obtained on the basis of the intervals between thesignal peak due to the stripe A₁ and the signal peak due to the stripeB₁, and the tape travelling speed (m/s). The intervals between the twosignal peaks are obtained on the basis of the shape of theabove-mentioned obtained reproduction waveform of the servo signal. Theabove-mentioned difference (B_(a1)-A_(a1)) corresponds to a differencebetween timings at which both the stripes are read at the actualtravelling position (actual path in FIG. 7 ) on the servo pattern of thereading element. Similarly, other difference terms can be obtained onthe basis of intervals between signal peaks due to two correspondingstripes, and the tape travelling speed. Further, the relative differencep is calculated similarly on the basis of the signal peak acquired bythe reading element b.

An azimuth angle φ in the above-mentioned calculation formula isobtained on the basis of the shape of the above-mentioned servo patternitself. The azimuth angle φ is obtained by developing the magnetic tapeMT with a ferricolloid developer (manufactured by SIGMA HI-CHEMICALINC., SigMarker Q) and using a universal tool microscope (TOPCONTUM-220ES) and a data processing apparatus (TOPCON CA-1B). Further, thedistance between the stripe A₁ and the strip B₁ (X in FIG. 7 and theabove-mentioned calculation formula) in the center of the servo band(center line in FIG. 7 ) and the distance between the stripe A₁ and thestrip C₁ (Y in FIG. 7 and the above-mentioned calculation formula) areobtained on the basis of the shape of the above-mentioned servo patternitself. Fifty servo frames are selected at arbitrary locations in thetape length direction, X and Y are obtained in each servo frame, andthose obtained by simply averaging 50 pieces of data are taken as X andY used in the above-mentioned calculation formula.

The relative difference p is calculated for each of 1024 consecutiveservo subframes along the longitudinal direction of the magnetic tapeMT. That is, 1024 relative differences p are acquired. For example, inthe case where the intervals between servo subframes are 76 μm, therelative difference p is acquired every 76 μm. The 1024 relativedifferences p calculated on the basis of the servo signal read by thereading element a will be referred to as pa₀, pa₁, . . . , and pa₁₀₂₃.The 1024 relative differences p calculated on the basis of the servosignal read by the reading element b will be referred to as pb₀, pb₁, .. . , and pb₁₀₂₃.

In order to eliminate the influence of the movement of the magnetic tapeMT in the width direction on the magnetic head, a difference between paand pb at each position n is calculated as Δp. That is,Δp_(n)=pa_(n)−pb_(n). Here, n=0, 1, . . . , and 1023. Discrete FFT(Fourier transform) is performed on the obtained Δp_(n) to obtain Δp_(n)(n=0 . . . 1023), i.e., ΔP(f) (where f=wave number [cycle/m]). Here, inorder to remove the DC component (i.e., n=0) of Δp_(n), in other words,ΔP(∞), ΔP₀ is replaced with a numerical value substantially close to 0such as 10⁻¹⁰⁰.

Further, the above-mentioned FFT is performed so that the unit of ΔP(f)is [nm²/Hz].

The process of obtain ΔP(f) is repeated in the longitudinal direction ofthe magnetic tape MT over 500 m or more to obtain ΔP(f)₁ . . .ΔP(f)_(m). In order to remove measurement noise, ΔP(f)₁ . . . ΔP(f)_(m)are averaged on the frequency axis to obtain ΔP(f)_(ave). After that, inorder to estimate behavior WIP(f) of the above-mentioned displacementdifference during actual drive, a general second-order closed-loopresponse filter CLF(f) is applied to ΔP(f)_(ave). That is,WIP(f)=|CLF(f)|²×ΔP(f)_(ave). CLF(f) will be described below.

Calculation of the following formula (1) is performed using theabove-mentioned WIP(f) to obtain σ_(SW). Also df in the followingcalculation will be described below. (Math. 2)σ_(SW)=√{square root over (ΣWIP(f)×df)}  (1)

The general second-order closed-loop response CLF(s) can be representedby the following formula (2).

$\begin{matrix}\left( {{Math}.\mspace{14mu} 3} \right) & \; \\{{{CLF}(s)} = \frac{s^{2}}{s^{2} + {2s\;\zeta\mspace{14mu}\omega_{0}} + \omega_{0}^{2}}} & (2)\end{matrix}$

By using bilinear Z transformation, CLF(z) can be represented by thefollowing formula (3).

$\begin{matrix}\left( {{Math}.\mspace{14mu} 4} \right) & \; \\{{{CLF}(z)} = \frac{K_{1}\mspace{14mu}\left( {z - 1} \right)^{2}}{z^{2} + {K_{2}z} + K_{3}}} & (3)\end{matrix}$

From the relationship of z=e^(jωTs) and ω=2πf, CLF(f) can be representedby the following formula (4).

$\begin{matrix}\left( {{Math}.\mspace{14mu} 5} \right) & \; \\{{{CLF}(f)} = \frac{K_{1}\mspace{14mu}\left( {e^{{j{({2\;\pi\; f})}}{Ts}} - 1} \right)^{2}}{e^{\;_{2{j{({2\pi\; f})}}{Ts}}} + {K_{2}e^{{j{({2\;\pi\; f})}}{Ts}}} + K_{3}}} & (4)\end{matrix}$

The meaning of each term in the formulae described above is as follows.

$\begin{matrix}{{{Ts}\text{:}\mspace{14mu}{Data}\mspace{14mu}{{interval}\mspace{14mu}\left\lbrack {m\text{/}{cycle}} \right\rbrack}} = {76 \times 1{0^{6}\left\lbrack {m\text{/}{cycle}} \right\rbrack}}} & \left( {{Math}.\mspace{14mu} 6} \right) \\{j\text{:}\mspace{14mu}{Imaginary}\mspace{14mu}{unit}} & \; \\{K_{1} = {{\frac{K_{s}^{2}}{K_{s}^{2} + {2\zeta\omega_{0}K_{s}} + \omega_{0}^{2}}\mspace{14mu} K_{s}} = {2F_{s}}}} & \; \\{K_{2} = {{\frac{2\mspace{14mu}\left( {\omega_{0}^{2} - K_{s}^{2}} \right)}{K_{s}^{2} + {2\zeta\omega_{0}K_{s}} + \omega_{0}^{2}}\mspace{14mu}\omega_{0}} = {2\;\pi\; F_{0}}}} & \; \\{K_{3} = {{\frac{K_{s}^{2} - {2\zeta\omega_{0}K_{s}} + \omega_{0}^{2}}{K_{s}^{2} + {2\zeta\omega_{0}K_{s}} + \omega_{0}^{2}}\mspace{14mu} F_{0}} = \ {F_{r}\sqrt{1 - {2\;\zeta^{2}}}}}} & \; \\{\zeta = \sqrt{\frac{1 - \sqrt{1 - \frac{1}{{MP}^{2}}}}{2}}} & \; \\{{F_{S}\left\lbrack {{cycle}\text{/}m} \right\rbrack} = {{1/T_{s}} = {13157.9\mspace{14mu}\left\lbrack {{cycle}\text{/}m} \right\rbrack}}} & \; \\{{d_{f}\text{:}\mspace{14mu}{Wave}\mspace{14mu}{number}\mspace{14mu}{{interval}\left\lbrack {{cycle}\text{/}m} \right\rbrack}} = {\frac{F_{S}/2}{102{4/2}} = {12.850\mspace{14mu}\left\lbrack {{cycle}\text{/}m} \right\rbrack}}} & \; \\{{F_{r}:\mspace{14mu}{{Peak}\mspace{14mu}{wave}\mspace{14mu}{number}\mspace{14mu}{of}\mspace{14mu}{{filter}\mspace{14mu}\left\lbrack {{cycle}\text{/}m} \right\rbrack}}} = 410} & \; \\{{{MP}\text{:}\mspace{14mu}{Filter}\mspace{14mu}{{gain}\mspace{14mu}\left\lbrack {a.u.} \right\rbrack}} = 10^{({1{{0{\lbrack{dB}\rbrack}}/20}})}} & \;\end{matrix}$

The upper limit value of an average thickness t_(m) of the magneticlayer 43 is 80 nm or less, favorably 70 nm or less, and more favorably50 nm or less. In the case where the upper limit value of the averagethickness t_(m) of the magnetic layer 43 is 80 nm or less, since theinfluence of a demagnetizing field can be reduced when a ring-type headis used as a recording head, further excellent electromagneticconversion characteristics can be achieved.

The lower limit value of the average thickness t_(m) of the magneticlayer 43 is favorably 35 nm or more. In the case where the lower limitvalue of the average thickness t_(m) of the magnetic layer 43 is 35 nmor more, since output can be secured when an MR-type head is used as areproduction head, further excellent electromagnetic conversioncharacteristics can be achieved.

The average thickness t_(m) of the magnetic layer 43 is obtained asfollows. First, the magnetic tape MT to be measured is processed by anFIB method or the like to make a slice. In the case of using an FIBmethod, as pretreatment for observing a TEM image of a cross sectiondescribed below, a carbon layer and a tungsten layer are formed asprotective films. The carbon layer is formed on surfaces of the magnetictape MT on the magnetic layer 43 side and on the back layer 44 side by adeposition method, and the tungsten layer is further formed on thesurface on the magnetic layer 43 side by a deposition method orsputtering method. The slicing is performed along the length direction(longitudinal direction) of the magnetic tape MT. That is, the slicingforms a cross section parallel to both the longitudinal direction andthe thickness direction of the magnetic tape MT.

The above-mentioned cross section of the obtained sliced sample isobserved with a transmission electron microscope (TEM) under thefollowing conditions to obtain a TEM image. Note that the magnificationand acceleration voltage may be appropriately adjusted depending on thetype of the apparatus.

Apparatus: TEM (H9000NAR manufactured by Hitachi. Ltd.)

Acceleration voltage: 300 kV

Magnification: 100,000

Next, the obtained TEM image is used for measuring the thickness of themagnetic layer 43 at at least 10 or more positions in the longitudinaldirection of the magnetic tape MT. The average value obtained by simplyaveraging (arithmetic average) the obtained measured values is taken asthe average thickness t_(m) [nm] of the magnetic layer 43. Note that theabove-mentioned measurement positions are randomly selected from thetest piece.

(Magnetic Powder)

The magnetic powder includes a plurality of magnetic particles. Themagnetic particles are, for example, particles containing hexagonalferrite (hereinafter, referred to as “hexagonal ferrite particles”),particles containing epsilon-type iron oxide (ε-iron oxide)(hereinafter, referred to as “ε-iron oxide particles”), or particlescontaining Co-containing spinel ferrite (hereinafter, referred to as“cobalt ferrite particles”). It is favorable that the magnetic powderhas crystal orientation preferentially in the thickness direction(vertical direction) of the magnetic tape MT.

(Hexagonal Ferrite Particles)

The hexagonal ferrite particles each have, for example, a plate shapesuch as a hexagon plate shape. In the present specification, the hexagonplate shape includes a substantially hexagon plate shape. The hexagonalferrite contains, favorably, at least one type of Ba, Sr, Pb, and Ca,more favorably, at least one type of Ba and Sr. Specifically, thehexagonal ferrite may be, for example, barium ferrite or strontiumferrite. The barium ferrite may further contain at least one type of Sr,Pb, and Ca in addition to Ba. The strontium ferrite may further containat least one type of Ba, Pb, and Ca in addition to Sr.

More specifically, the hexagonal ferrite has an average compositionrepresented by the general formula MFe₁₂O₁₉. However, M is, for example,at least one type of metal of Ba, Sr, Pb, and Ca, favorably at least onetype of meatal of Ba and Sr. M may be a combination of Ba and one ormore types of metal selected from the group consisting of Sr, Pb, andCa. Further, M may be a combination of Sr and one or more types of metalselected from the group consisting of Ba, Pb, and Ca. Some Fe in theabove-mentioned general formula may be substituted with another metalelement.

In the case where the magnetic powder includes hexagonal ferriteparticles, the average particle size of the magnetic powder is favorably30 nm or less, more favorably 12 nm or more and 25 nm or less, stillmore favorably 15 nm or more and 22 nm or less, particularly favorably15 nm or more and 20 nm or less, and most favorably 15 nm or more and 18nm or less. In the case where the average particle size of the magneticpowder is 30 nm or less, the further excellent electromagneticconversion characteristics (e.g., SNR) can be achieved in the magnetictape MT having a high recording density. Meanwhile, in the case wherethe average particle size of the magnetic powder is 12 nm or more, thedispersibility of the magnetic powder is enhanced, and further excellentelectromagnetic conversion characteristics (e.g., SNR) can be achieved.

The average aspect ratio of the magnetic powder is favorably 1.0 or moreand 2.5 or less, more favorably 1.0 or more and 2.1 or less, and stillmore favorably 1.0 or more and 1.8 or less. In the case where theaverage aspect ratio of the magnetic powder is within the range of 1.0or more and 2.5 or less, aggregation of the magnetic powder can besuppressed. Further, the resistance applied to the magnetic powder whenthe magnetic powder is vertically oriented in the process of forming themagnetic layer 43 can be reduced. Therefore, the vertical orientation ofthe magnetic powder can be improved.

In the case where the magnetic powder includes hexagonal ferriteparticles, the average particle size and the average aspect ratio of themagnetic powder are obtained as follows. First, the magnetic tape MT tobe measured is processed by an FIB method or the like to make a slice.In the case of using an FIB method, as pretreatment for observing a TEMimage of a cross section described below, a carbon layer and a tungstenlayer are formed as protective films. The carbon layer is formed onsurfaces of the magnetic tape MT on the magnetic layer 43 side and onthe back layer 44 side by a deposition method, and the tungsten layer isfurther formed on the surface on the magnetic layer 43 side by adeposition method or sputtering method. The slicing is performed alongthe length direction (longitudinal direction) of the magnetic tape MT.That is, the slicing forms a cross section parallel to both thelongitudinal direction and the thickness direction of the magnetic tapeMT.

The above-mentioned cross section of the obtained slice sample isobserved at an acceleration voltage: 200 kV and the total magnificationof 500,000 using a transmission electron microscope (H-9500 manufacturedby Hitach High-Technologies Corporation) so that the entire magneticlayer 43 is included in the thickness direction of the magnetic layer43, and a TEM photograph is taken. Next, 50 particles with the sidefacing in the direction of the observation surface, whose particlethickness can be clearly observed, are selected from the taken TEMphotograph. For example, Part A of FIG. 9 and Part B of FIG. 9 each showan example of the TEM photograph. In Part A of FIG. 9 and Part B of FIG.9 , for example, particles indicated by arrows a and d are selectedbecause the thickness of each of the particles can be clearly observed.The maximum thickness DA of each of the 50 selected particles ismeasured. The maximum thicknesses DA thus obtained are simply averaged(arithmetic average) to obtain an average maximum thickness DA_(ave).Subsequently, the plate diameter DB of each magnetic powder is measured.In order to measure the plate diameter DB of the particle, 50 particlesin which the plate diameter of the particle can be clearly observed areselected from the taken TEM photograph. For example, in Part A of FIG. 9and Part B of FIG. 9 , for example, particles indicated by arrows b andc are selected because the plate diameter of the particle can be clearlyobserved. The plate diameter DB of each of the 50 selected particles ismeasured. The plate diameters DB thus obtained are simply averaged(arithmetic average) to obtain an average plate diameter DB_(ave). Theaverage plate diameter DB_(ave) is an average particle size. Then, onthe basis of from the average maximum thickness DA_(ave) and the averageplate diameter DB_(ave), the average aspect ratio (DB_(ave)/DA_(ave)) ofthe particles is obtained.

In the case where the magnetic powder includes hexagonal ferriteparticles, the average particle volume of the magnetic powder isfavorably 5900 nm³ or less, more favorably 500 nm³ or more and 3400 nm³or less, still more favorably 1000 nm³ or more and 2500 nm³ or less,particularly favorably 1000 nm³ or more and 1800 nm³ or less, and mostfavorably 1000 nm³ or more and 1500 nm³ or less. In the case where theaverage particle volume of the magnetic powder is 5900 nm³ or less,effects similar to those in the case where the average particle size ofthe magnetic powder is 30 nm or less can be achieved. Meanwhile, in thecase where the average particle volume of the magnetic powder is 500 nm³or more, effects similar to those in the case where the average particlesize of the magnetic powder is 12 nm or more can be achieved.

The average particle volume of the magnetic powder is obtained asfollows. First, as described in the above-mentioned method ofcalculating the average particle size of the magnetic powder, an averagemajor axis length DA_(ave) and the average plate diameter DB_(ave) areobtained. Next, an average volume V of the magnetic powder is obtainedusing the following formula.

$\begin{matrix}{V = {\frac{3\sqrt{3}}{8} \times DA_{ave} \times DB_{ave} \times DB_{ave}}} & \left( {{Math}.\mspace{14mu} 7} \right)\end{matrix}$

(ε-Iron Oxide Particle)

The ε-iron oxide particles are hard magnetic particles that can achievea high coercive force even with fine particles. The ε-iron oxideparticles each have a spherical shape or a cubic shape. In the presentspecification, the spherical shape includes a substantially sphericalshape. Further, the cubic shape includes a substantially cubic shape.Since the ε-iron oxide particles each have the above-mentioned shape, inthe case where ε-iron oxide particles are used as the magneticparticles, the contact area between particles in the thickness directionof the magnetic tape MT is reduced and aggregation of particles can besuppressed as compared with the case where barium ferrite particles eachhaving a hexagon plate shape are used as the magnetic particles.Therefore, it is possible to enhance the dispersibility of the magneticpowder and achieved further excellent electromagnetic conversioncharacteristics (e.g., SNR).

The ε-iron oxide particles each have a core-shell structure.Specifically, the ε-iron oxide particle includes a core portion and ashell portion that is provided around the core portion and has a 2-layerstructure. The shell portion having the 2-layer structure includes afirst shell portion provided on the core portion, and a second shellportion provided on the first shell portion.

The core portion contains ε-iron oxide. The ε-iron oxide contained inthe core portion favorably has an ε-Fe₂O₃ crystal as a main phase, andis more favorably formed of a single phase of ε-Fe₂O₃.

The first shell portion covers at least a part of the periphery of thecore portion. Specifically, the first shell portion may partially coverthe periphery of the core portion or may cover the entire periphery ofthe core portion. It is favorable that the entire surface of the coreportion is covered from the viewpoint of making the exchange couplingbetween the core portion and the first shell portion sufficient andimproving the magnetic properties.

The first shell portion is a so-called soft magnetic layer, andcontains, for example, a soft magnetic material such as α-Fe, an Ni—Fealloy, and an Fe—Si—Al alloy. α-Fe may be one obtained by reducingε-iron oxide contained in the core portion.

The second shell portion is an oxide coating film as an oxidationprevention layer. The second shell portion contains α-iron oxide,aluminum oxide, or silicon oxide. The α-iron oxide contains, forexample, at least one iron oxide of Fe₃O₄, Fe₂O₃, and FeO. In the casewhere the first shell portion contains α-Fe (soft magnetic material),the α-iron oxide may be one obtained by oxidizing α-Fe contained in thefirst shell portion.

Since the ε-iron oxide particle incudes the first shell portion asdescribed above, a coercive force Hc of the entire ε-iron oxide particle(core-shell particles) can be adjusted to the coercive force Hc suitablefor recording while maintaining the coercive force Hc of the coreportion alone to a large value to secure thermal stability. Further,since the ε-iron oxide particle includes the second shell portion asdescribed above, it is possible to prevent the characteristics of theε-iron oxide particle from being reduced due to occurrence of rust orthe like on the particle surface by exposure of the ε-iron oxideparticle to the air during and before the process of producing themagnetic tape MT. Therefore, it is possible to suppress characteristicdeterioration of the magnetic tape MT.

The ε-iron oxide particle may include a shell portion having asingle-layer structure. In this case, the shell portion has a structuresimilar to that of the first shell portion. However, from the viewpointof suppressing the characteristic deterioration of the ε-iron oxideparticle, it is favorable that the ε-iron oxide particle includes ashell portion having a 2-layer structure as described above.

The ε-iron oxide particle may contain an additive instead of theabove-mentioned core-shell structure, or may contain an additive inaddition to the core-shell structure. In this case, some Fe of theε-iron oxide is substituted with the additive. Also by causing theε-iron oxide particle to contain an additive, the coercive force Hc ofthe entire ε-iron oxide particle can be adjusted to the coercive forceHc suitable for recording, and thus, the ease of recording can beimproved. The additive is a metal element other than iron, favorably atrivalent metal element, more favorably at least one type of Al, Ga, andIn, and still more favorably at least one type of Al and Ga.

Specifically, the ε-iron oxide containing an additive is anε-Fe_(2-x)M_(x)O₃ crystal (in which M is a metal element other thaniron, favorably a trivalent metal element, more favorably at least onetype of Al, Ga, and In, and still more favorably at least one type of Aland Ga. x satisfies the relationship of, for example, 0<x<1).

The average particle size (average maximum particle size) of themagnetic powder is, for example, 22.5 nm or less. The average particlesize of (average maximum particle size) of the magnetic powder is,favorably, 22 nm or less, more favorably 8 nm or more and 22 nm or less,still more favorably 12 nm or more and 22 nm or less, particularlyfavorably 12 nm or more and 15 nm or less, and most favorably 12 nm ormore and 14 nm or less. In the magnetic tape MT, a region having a sizeof half the recording wavelength is an actual magnetized region. Forthis reason, by setting the average particle size of the magnetic powderto half or less of the shortest recording wavelength, it is possible toachieve further excellent electromagnetic conversion characteristics(e.g., SNR). Therefore, in the case where the average particle size ofthe magnetic powder is 22 nm or less, further excellent electromagneticconversion characteristics (e.g., SNR) can be achieved in the magnetictape MT having a high recording density (e.g., the magnetic tape MTconfigured to be capable of recording a signal with the shortestrecording wavelength of 44 nm or less). Meanwhile, in the case where theaverage particle size of the magnetic powder is 8 nm or more, thedispersibility of the magnetic powder is further improved, and furtherexcellent electromagnetic conversion characteristics (e.g., SNR) can beachieved.

The average aspect ratio of the magnetic powder is favorably 1.0 or moreand 3.0 or less, more favorably 1.0 or more and 2.5 or less, still morefavorably 1.0 or more and 2.1 or less, and particularly favorably 1.0 ormore and 1.8 or less. In the case where the average aspect ratio of themagnetic powder is within the range of 1.0 or more and 3.0 or less,aggregation of the magnetic powder can be suppressed. Further, theresistance applied to the magnetic powder when the magnetic powder isvertically oriented in the process of forming the magnetic layer 43 canbe reduced. Therefore, it is possible to improve the verticalorientation of the magnetic powder.

In the case where the magnetic powder contains ε-iron oxide particles,the average particle size and the average aspect ratio of the magneticpowder are obtained as follows. First, the magnetic tape MT to bemeasured is processed by an FIB (Focused Ion Beam) method or the like tomake a slice. In the case of using an FIB method, as pretreatment forobserving a TEM image of a cross section described below, a carbon layerand a tungsten layer are formed as protective films. The carbon layer isformed on surfaces of the magnetic tape MT on the magnetic layer 43 sideand on the back layer 44 side by a deposition method, and the tungstenlayer is further formed on the surface on the magnetic layer 43 side bya deposition method or sputtering method. The slicing is performed alongthe length direction (longitudinal direction) of the magnetic tape MT.That is, the slicing forms a cross section parallel to both thelongitudinal direction and the thickness direction of the magnetic tapeMT.

The above-mentioned cross section of the obtained slice sample isobserved at an acceleration voltage: 200 kV and the total magnificationof 500,000 using a transmission electron microscope (H-9500 manufacturedby Hitach High-Technologies Corporation) so that the entire magneticlayer 43 is included in the thickness direction of the magnetic layer43, and a TEM photograph is taken. Next, 50 particles in which the shapeof the particle can be clearly observed are selected from the taken TEMphotograph, and a major axis length DL and a minor axis length DS ofeach of the particles are measured. Here, the major axis length DL meansthe largest one (so-called maximum Feret diameter) of distances betweentwo parallel lines drawn from all angles so as to contact the outline ofeach particle. Meanwhile, the minor axis length DS means the largest oneof lengths of the particle in the direction perpendicular to the majoraxis (DL) of the particle. Subsequently, the major axis lengths DL ofthe 50 measured particles are simply averaged (arithmetic average) toobtain an average major axis length DL_(ave). The average major axislength DL_(ave) thus obtained is taken as the average particle size ofthe magnetic powder. Further, the minor axis lengths DS of the 50measured particles are simply averaged (arithmetic average) to obtain anaverage minor axis length DS_(ave). Then, on the basis of the averagemajor axis length DL_(ave) and the average minor axis length DS_(ave),the average aspect ratio (DL_(ave)/DS_(ave)) of the particles isobtained.

The average particle volume of the magnetic powder is favorably 5600 nm³or less, more favorably 250 nm³ or more and 5600 nm³ or less, still morefavorably 900 nm³ or more and 5600 nm³ or less, particularly favorably900 nm³ or more and 1800 nm³ or less, most favorably 900 nm³ or more and1500 nm³ or less. In general, since noise of the magnetic tape MT isinversely proportional to the square root of the number of particles(i.e., proportional to the square root of the particle volume), furtherexcellent electromagnetic conversion characteristics (e.g., SNR) can beachieved by reducing the particle volume. Therefore, in the case wherethe average particle volume of the magnetic powder is 5600 nm³ or less,further excellent electromagnetic conversion characteristics (e.g., SNR)can be obtained similarly in the case where the average particle size ofthe magnetic powder is 22 nm or less. Meanwhile, in the case where theaverage particle volume of the magnetic powder is 250 nm³ or more,effects similar to those in the case where the average particle size ofthe magnetic powder is 8 nm or more are obtained.

In the case where the ε-iron oxide particle has a spherical shape, theaverage particle volume of the magnetic powder is obtained as follows.First, similarly to the above-mentioned method of calculating theaverage particle size of the magnetic powder, the average major axislength DL_(ave) is obtained. Next, the average volume V of the magneticpowder is obtained using the following formula.V=(π/6)×DLave³

In the case where the ε-iron oxide particle has a cubic shape, theaverage volume of the magnetic powder is obtained as follows. Themagnetic tape MT is processed by an FIB (Focused Ion Beam) method or thelike to make a slice. In the case of using an FIB method, aspretreatment for observing a TEM image of a cross section describedbelow, a carbon film and a tungsten thin film are formed as protectivefilms. The carbon film is formed on surfaces of the magnetic tape MT onthe magnetic layer 43 side and on the back layer 44 side by a depositionmethod, and the tungsten thin film is further formed on the surface onthe magnetic layer 43 side by a deposition method or sputtering method.The slicing is performed along the length direction (longitudinaldirection) of the magnetic tape MT. That is, the slicing forms a crosssection parallel to both the longitudinal direction and the thicknessdirection of the magnetic tape MT.

The above-mentioned cross section of the obtained slice sample isobserved at an acceleration voltage: 200 kV and the total magnificationof 500,000 using a transmission electron microscope (H-9500 manufacturedby Hitach High-Technologies Corporation) so that the entire magneticlayer 43 is included in the thickness direction of the magnetic layer43, and a TEM photograph is taken. Note that the magnification andacceleration voltage may be appropriately adjusted depending on the typeof the apparatus. Next, 50 particles in which the shape of the particleis clear are selected from the taken TEM photograph, and a side lengthDC of each particle is measured. Subsequently, the side lengths DC ofthe 50 measured particles are simply averaged (arithmetic average) toobtain an average side length DC_(ave). Next, the average volume V_(ave)(particle volume) of the magnetic powder is obtained on the basis of thefollowing formula using the average side length DC_(ave).V _(ave) =DC _(ave) ³

(Cobalt Ferrite Particles)

The cobalt ferrite particles favorably have uniaxial crystal anisotropy.In the case where the cobalt ferrite particles have uniaxial crystalanisotropy, it is possible to cause the magnetic powder to have crystalorientation preferentially in the thickness direction (verticaldirection) of the magnetic tape MT. The cobalt ferrite particles eachhave, for example, a cubic shape. In the present specification, thecubic shape includes a substantially cubic shape. The Co-containingspinel ferrite may further contain at least one type of Ni, Mn, Al, Cu,and Zn in addition to Co.

The Co-containing spinel ferrite has, for example, an averagecomposition represented by the following formula.

Co_(x)M_(y)Fe₂O_(Z)

(in which M is, for example, at least one type of metal of Ni, Mn, Al,Cu, and Zn. x is a value within the range of 0.4≤x≤1.0. y is a valuewithin the range of 0≤y≤0.3. However, x and y satisfy the relationshipof (x+y)≤1.0. z is a value within the range of 3≤z≤4. Some Fe may besubstituted with another metal element.)

In the case where the magnetic powder contains the cobalt ferriteparticles, the average particle size of the magnetic powder is favorably25 nm or less, more favorably 8 nm or more and 23 nm or less, still morefavorably 8 nm or more and 12 nm or less, and particularly favorably 8nm or more and 11 nm or less. In the case where the average particlesize of the magnetic powder is 25 nm or less, further excellentelectromagnetic conversion characteristics (e.g., SNR) can be achievedin the magnetic tape MT having a high recording density. Meanwhile, inthe case where the average particle size of the magnetic powder is 8 nmor more, the dispersibility of the magnetic powder is further enhancedand further excellent electromagnetic conversion characteristics (e.g.,SNR) can be achieved. The method of calculating the average particlesize of the magnetic powder is similar to the method of calculating theaverage particle size of the magnetic powder in the case where themagnetic powder contains ε-iron oxide particle powder.

The average aspect ratio of the magnetic powder is favorably 1.0 or moreand 3.0 or less, more favorably 1.0 or more and 2.5 or less, still morefavorably 1.0 or more and 2.1 or less, and particularly favorably 1.0 ormore and 1.8 or less. In the case where the average aspect ratio of themagnetic powder is within the range of 1.0 or more and 3.0 or less,aggregation of the magnetic powder can be suppressed. Further, theresistance applied to the magnetic powder when the magnetic powder isvertically oriented in the process of forming the magnetic layer 43 canbe reduced. Therefore, it is possible to improve the verticalorientation of the magnetic powder. The method of calculating theaverage aspect ratio of the magnetic powder is similar to the method ofcalculating the average aspect ratio of the magnetic powder in the casewhere the magnetic powder contains ε-iron oxide particle powder.

The average particle volume of the magnetic powder is favorably 15000nm³ or less, more favorably 500 nm³ or more and 12000 nm³ or less,particularly favorably 500 nm³ or more and 1800 nm³ or less, and mostfavorably 500 nm³ or more and 1500 nm³ or less. In the case where theaverage particle volume of the magnetic powder is 15000 nm³ or less,effects similar to those in the case where the average particle size ofthe magnetic powder is 25 nm or less can be achieved. Meanwhile, in thecase where the average particle volume of the magnetic powder is 500 nm³or more, effects similar to those in the case where the average particlesize of the magnetic powder is 8 nm or more can be achieved. The methodof calculating the average particle volume of the magnetic powder issimilar to the method of calculating the average particle volume in thecase where the ε-iron oxide particle has a cubic shape.

(Binder)

Examples of the binder include a thermoplastic resin, a thermosettingresin, and a reactive resin. Examples of the thermoplastic resin includevinyl chloride, vinyl acetate, a vinyl chloride-vinyl acetate copolymer,a vinyl chloride-vinylidene chloride copolymer, a vinylchloride-acrylonitrile copolymer, an acrylate ester-acrylonitrilecopolymer, an acrylate ester-vinyl chloride-vinylidene chloridecopolymer, an acrylate ester-acrylonitrile copolymer, an acrylateester-vinylidene chloride copolymer, a methacrylic acid ester-vinylidenechloride copolymer, a methacrylic acid ester-vinyl chloride copolymer, amethacrylic acid ester-ethylene copolymer, polyvinyl fluoride, avinylidene chloride-acrylonitrile copolymer, an acrylonitrile-butadienecopolymer, a polyamide resin, polyvinyl butyral, a cellulose derivative(cellulose acetate butyrate, cellulose diacetate, cellulose triacetate,cellulose propionate, nitrocellulose), a styrene butadiene copolymer, apolyurethane resin, a polyester resin, an amino resin, and syntheticrubber.

Examples of the thermosetting resin include a phenol resin, an epoxyresin, a polyurethane curable resin, a urea resin, a melamine resin, analkyd resin, a silicone resin, a polyamine resin, and a ureaformaldehyde resin.

In order to improve the dispersibility of the magnetic powder, polarfunctional groups such as —SO₃M, —OSO₃M, —COOM, P═O(OM)₂ (in which M inthe formula represents a hydrogen atom or an alkali metal such aslithium, potassium, and sodium), a side-chain amine having a terminalgroup represented by —NR1R2 or —NR1R2R3⁺X⁻, a main-chain aminerepresented by >NR1R2⁺X⁻ (in which R1, R2, and R3 in the formula eachrepresent a hydrogen atom or a hydrocarbon group, and X⁻ represents ahalogen element ion such as fluorine, chlorine, bromine, and iodine, oran inorganic or organic ion), —OH, —SH, —CN, and an epoxy group may beintroduced into all the above-mentioned binders. The amount of polarfunctional groups introduced into the binder is favorably 10⁻¹ to 10⁻⁸mol/g and more favorably 10⁻² to 10⁻⁶ mol/g.

(Lubricant)

The lubricant contains, for example, at least one type selected fromfatty acids and fatty acid esters, favorably, both a fatty acid, and afatty acid ester. The magnetic layer 43 contains a lubricant,particularly, the magnetic layer 43 contains both a fatty acid and afatty acid ester, which contributes to improvement of travellingstability of the magnetic tape MT. In more particular, the magneticlayer 43 contains a lubricant and includes pores, thereby achievingfavorable travelling stability. The improvement in the travellingstability is because the dynamic friction coefficient on the surface ofthe magnetic tape MT on the magnetic layer 43 side is adjusted with theabove-mentioned lubricant to a value suitable for travelling of themagnetic tape MT.

The fatty acid may favorably be a compound represented by the followinggeneral formula (1) or (2). For example, as a fatty acid, one of acompound represented by the following formula (1) and a compoundrepresented by the following formula (2) or both of them may becontained.

Further, the fatty acid ester may favorably be a compound represented bythe following general formula (3) or (4). For example, as a fatty acidester, one of a compound represented by the following formula (3) and acompound represented by the following formula (4) or both of them may becontained.

In the case where the lubricant contains one of the compound representedby the following formula (1) and the compound represented by thefollowing formula (2) or both of them, and one of the compoundrepresented by the following formula (3) and the compound represented bythe following formula (4) or both of them, which makes it possible tosuppress the increase in the dynamic friction coefficient due torepeated recording or reproduction of the magnetic tape MT.CH₃(CH₂)_(k)COOH  (1)

(in which in the general formula (1), k is an integer selected from therange of 14 or more and 22 or less, more favorably 14 or more and 18 orless.)CH₃(CH₂)_(n)CH═CH(CH₂)_(m)COOH  (2)

(in which in the general formula (2), the sum of n and m is an integerselected from the range of 12 or more and 20 or less, more favorably 14or more and 18 or less.)CH₃(CH₂)_(p)COO(CH₂)_(q)CH₃  (3)

(in which in the general formula (3), p is an integer selected from therange of 14 or more and 22 or less, more favorably 14 or more and 18 orless, and q is an integer selected from the range of 2 or more and 5 orless, more favorably 2 or more and 4 or less.)CH₃(CH₂)_(r)COO—(CH₂)_(s)CH(CH₃)₂  (4)

(in which in the general formula (4), r is an integer selected from therange of 14 or more and 22 or less, and s is an integer selected fromthe range of 1 or more and 3 or less.)

(Antistatic Agent)

Examples of the antistatic agent include carbon black, a naturalsurfactant, a nonionic surfactant, and a cationic surfactant.

(Abrasive)

Examples of the abrasive include α-alumina with an alpha conversion rateof 90% or more, β-alumina, γ-alumina, silicon carbide, chromium oxide,cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide,titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungstenoxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate,calcium sulfate, barium sulfate, molybdenum disulfide, needle-likeα-iron oxide obtained by dehydrating and annealing magnetic iron oxideraw material, and those obtained by performing surface treatment thereonwith aluminum and/or silica as necessary.

(Curing Agent)

Examples of the curing agent include polyisocyanate. Examples ofpolyisocyanate include an aromatic polyisocyanate such as an adduct oftolylene diisocyanate (TDI) with an active hydrogen compound, and analiphatic polyisocyanate such as an adduct of hexamethylene diisocyanate(HMDI) with an active hydrogen compound. The weight average molecularweight of the polyisocyanates is favorably within the range of 100 to3000.

(Rust Inhibitor)

Examples of the rust inhibitor include phenols, naphthols, quinones,heterocyclic compounds containing a nitrogen atom, heterocycliccompounds containing an oxygen atom, and heterocyclic compoundscontaining a sulfur atom.

(Non-Magnetic Reinforcing Particle)

Examples of the non-magnetic reinforcing particle include aluminum oxide(α, β, or γ alumina), chromium oxide, silicon oxide, diamond, garnet,emery, boron nitride, titanium carbide, silicon carbide, titaniumcarbide, and titanium oxide (rutile or anatase titanium oxide).

(Underlayer)

The underlayer 42 is for alleviating the unevenness of the surface ofthe substrate 41 to adjust the unevenness of the surface of the magneticlayer 43. The underlayer 42 is a non-magnetic layer containing anon-magnetic powder, a binder, and a lubricant. The underlayer 42supplies a lubricant to the surface of the magnetic layer 43. Theunderlayer 42 may further contain, as necessary, at least one additiveof an antistatic agent, a curing agent, and a rust inhibitor.

The average thickness of the underlayer 42 is favorably 0.3 μm or moreand 2.0 μm or less, more favorably 0.5 μm or more and 1.4 μm or less.Note that the average thickness of the underlayer 42 is obtained in asimilar way as the average thickness of the magnetic layer 43. However,the magnification of the TEM image is appropriately adjusted inaccordance with the thickness of the underlayer 42. In the case wherethe average thickness of the underlayer 42 is 2.0 μm or less, theexpansion/contraction property of the magnetic tape MT due to anexternal force is further enhanced, which makes it easier to adjust thewidth of the magnetic tape MT by tension adjustment.

It is favorable that the underlayer 42 includes a large number of holes.By causing the holes to store a lubricant, it is possible to furthersuppress the decrease in the amount of lubricant supplied between thesurface of the magnetic layer 43 and the magnetic head even afterrepeatedly performing recording or reproduction (i.e., even after themagnetic tape MT is caused to repeatedly travel while the magnetic head56 is in contact with the surface of the magnetic tape MT). Therefore,it is possible to further suppress the increase in the dynamic frictioncoefficient. That is, further excellent travelling stability can beachieved.

From the viewpoint of suppressing the decrease in the dynamic frictioncoefficient after repeated recording or reproduction, it is favorablethat the holes of the underlayer 42 and the holes 43A of the magneticlayer 43 are connected to each other. Here, “the holes of the underlayer42 and the holes 43A of the magnetic layer 43 are connected to eachother” includes the state where some of the holes of the underlayer 42and some of the holes 43A of the magnetic layer 43 are connected to eachother.

From the viewpoint of improving supply of the lubricant to the surfaceof the magnetic layer 43, it is favorable that the holes include thoseextending in the direction perpendicular to the surface of the magneticlayer 43. Further, from the viewpoint of improving supply of thelubricant to the surface of the magnetic layer 43, the holes of theunderlayer 42 extending in the direction perpendicular to the surface ofthe magnetic layer 43 and the holes 43A of the magnetic layer 43extending in the direction perpendicular to the surface of the magneticlayer 43 are connected to each other.

(Non-Magnetic Powder)

The non-magnetic powder contains, for example, at least one type of aninorganic particle powder or an organic particle powder. Further, thenon-magnetic powder may contain a carbon powder such as carbon black.Note that one type of the non-magnetic powder may be used alone, or twoor more types of the non-magnetic powder may be used in combination. Theinorganic particle contains, for example, a metal, a metal oxide, ametal carbonate, a metal sulfate, a metal nitride, a metal carbide, or ametal sulfide. Examples of the shape of the non-magnetic powder include,but not limited to, various shapes such as a needle shape, a sphericalshape, a cubic shape, and a plate shape.

Examples of the shape of the non-magnetic powder include, but notlimited to, various shapes such as a needle shape, a spherical shape, acubic shape, and a plate shape.

(Binder and Lubricant)

The binder and the lubricant are similar to those of the above-mentionedmagnetic layer 43.

(Additive)

The antistatic agent, the curing agent, and the rust inhibitor aresimilar to those of the above-mentioned magnetic layer 43.

(Back Layer)

The back layer 44 contains a binder and a non-magnetic powder. The backlayer 44 may further contain, as necessary, at least one additive of alubricant, a curing agent, or an antistatic agent. The binder and thenon-magnetic powder are similar to those of the above-mentionedunderlayer 42.

The average particle size of the non-magnetic powder is favorably 10 nmor more and 150 nm or less, more favorably 15 nm or more and 110 nm orless. The average particle size of the non-magnetic powder is obtainedin a similar way to the above-mentioned average particle size of themagnetic powder. The non-magnetic powder may contain a non-magneticpowder having two or more types of particle size distribution.

The upper limit value of the average thickness of the back layer 44 isfavorably 0.6 μm or less. In the case where the upper limit value of theaverage thickness of the back layer 44 is 0.6 μm or less, the thicknessof the underlayer 42 or the substrate 41 can be kept thick even in thecase where the average thickness of the magnetic tape MT is 5.6 μm orless. Therefore, the travelling stability of the magnetic tape MT in therecording/reproduction apparatus 50 can be maintained. The lower limitvalue of the average thickness of the back layer 44 is not particularlylimited, but is, for example, 0.2 μm or more.

An average thickness t_(b) of the back layer 44 is obtained as follows.First, an average thickness t_(T) of the magnetic tape MT is measured.The method of measuring the average thickness t_(T) is as described inthe following “Average Thickness of Magnetic Tape”. Subsequently, theback layer 44 of the sample is removed with a solvent such as MEK(methyl ethyl ketone) and dilute hydrochloric acid. Next, the laserhologauge (LGH-110C) manufactured by Mitsutoyo Corporation is used formeasuring the thickness of the sample at five or more points, and themeasured values are simply averaged (arithmetic average) to calculate anaverage value t_(B)[μm]. After that, the average thickness t_(b)[μm] ofthe back layer 44 is obtained using the following formula. Note that themeasurement positions are randomly selected from the sample.t _(b)[μM]=t _(T)[μM]−t _(B)[μm]

The back layer 44 has a surface on which a large number of protrusions44A is provided. The protrusions 44A are for forming the holes 43A onthe surface of the magnetic layer 43 in the state where the magnetictape MT is wound up in a roll shape. The holes 43A include, for example,a large number of non-magnetic particles protruding from the surface ofthe back layer 44.

(Average Thickness of Magnetic Tape)

The upper limit value of the average thickness (average total thickness)t_(T) of the magnetic tape MT is 5.6 μm or less, favorably 5.0 μm orless, more favorably 4.6 μm or less, and still more favorably 4.4 μm orless. In the case where the average thickness t_(T) of the magnetic tapeMT is 5.6 μm or less, the recording capacity of one data cartridge canbe increased as compared with that of a general magnetic tape. The lowerlimit value of the average thickness t_(T) of the magnetic tape MT isnot particularly limited, but is, for example, 3.5 μm or more.

The average thickness t_(T) of the magnetic tape MT is obtained asfollows. First, the magnetic tape MT having a width of ½ inch isprepared and cut into a 250 mm length to prepare a sample. Next, thethickness of the sample is measured at five or more points by using thelaser hologauge (LGH-110C) manufactured by Mitsutoyo Corporation as ameasurement apparatus, and the measured values are simply averaged(arithmetic average) to calculate the average value t_(T)[μm]. Note thatthe measurement positions are randomly selected from the sample.

(Coercive Force Hc)

The upper limit value of a coercive force Hc2 of the magnetic layer 43in the longitudinal direction of the magnetic tape MT is favorably 2000Oe or less, more favorably 1900 Oe or less, and still more favorably1800 Oe or less. In the case where the coercive force Hc2 of themagnetic layer 43 in the longitudinal direction is 2000 Oe or less,sufficient electromagnetic conversion characteristics while having ahigh recording density can be achieved.

The lower limit value the coercive force Hc2 of the magnetic layer 43measured in the longitudinal direction of the magnetic tape MT isfavorably 1000 Oe or more. In the case where the coercive force Hc2 ofthe magnetic layer 43 measured in the longitudinal direction is 1000 Oeor more, it is possible to suppress demagnetization due to leakage fluxfrom the recording head.

The above-mentioned coercive force Hc2 is obtained as follows. First,three magnetic tapes MT are overlapped with each other with double-sidedtapes, and then punched out with a φ6.39 mm punch to prepare ameasurement sample. At this time, marking is performed with an arbitraryink that does not have magnetism so that the longitudinal direction(travelling direction) of the magnetic tape MT can be recognized. Then,an M-H loop of the measurement sample (entire magnetic tape MT)corresponding to the longitudinal direction (travelling direction) ofthe magnetic tape MT is measured using a vibrating sample magnetometer(VSM). Next, the coating films (the underlayer 42, the magnetic layer43, the back layer 44, and the like) are wiped by using acetone,ethanol, or the like, leaving only the substrate 41. Then, the obtainedthree substrates 41 are overlapped with each other with double-sidedtapes, and then punched out with a φ6.39 mm punch to prepare a samplefor back ground correction (hereinafter, referred to simply as“correction sample”). After that, the M-H loop of the correction sample(substrate 41) corresponding to the vertical direction of the substrate41 (vertical direction of the magnetic tape MT) is measured using theVSM.

In measuring the M-H loop of the measurement sample (entire magnetictape MT) and the M-H loop of the correction sample (substrate 41), ahigh sensitivity vibrating sample magnetometer “VSM-P7-15” manufacturedby TOEI INDUSTRY CO., LTD. is used. The measurement conditions are ameasurement mode: full loop, the maximum magnetic field: 15 kOe, amagnetic field step: 40 bit, Time constant of Locking amp: 0.3 sec,Waiting time: 1 sec, and the average number of MH: 20.

After obtaining the M-H loop of the measurement sample (entire magnetictape MT) and the M-H loop of the correction sample (substrate 41),background correction is performed by subtracting the M-H loop of thecorrection sample (substrate 41) from the M-H loop of the measurementsample (entire magnetic tape MT) to obtain the M-H loop after the background correction. For the calculation of the back ground correction, ameasurement/analysis program attached to the “VSM-P7-15” is used. Thecoercive force Hc2 is obtained on the basis of the obtained M-H loopafter the back ground correction. Note that for this calculation, ameasurement/analysis program attached to the “VSM-P7-15” is used. Notethat all of the above-mentioned M-H loops are measured at 25° C.Further, “demagnetizing field correction” when measuring the M-H loop inthe longitudinal direction of the magnetic tape MT is not performed.

(Squareness Ratio)

A squareness ratio S1 of the magnetic layer 43 in the vertical direction(thickness direction) of the magnetic tape MT is favorably 65% or more,more favorably 70% or more, still more favorably 75% or more,particularly favorably 80% or more, and most favorably 85% or more. Inthe case where the squareness ratio S1 is 65% or more, since thevertical orientation of the magnetic powder is sufficiently high,further excellent electromagnetic conversion characteristics (e.g., SNR)can be achieved.

The squareness ratio S1 in the vertical direction is obtained asfollows. First, three magnetic tapes MT are overlapped with each otherwith double-sided tapes, and then punched out with a φ6.39 mm punch toprepare a measurement sample. At this time, marking is performed with anarbitrary ink that does not have magnetism so that the longitudinaldirection (travelling direction) of the magnetic tape MT can berecognized. Then, an M-H loop of the measurement sample (entire magnetictape MT) corresponding to the vertical direction (thickness direction)of the magnetic tape MT is measured using the VSM. Next, the coatingfilms (the underlayer 12, the magnetic layer 43, the back layer 44, andthe like) are wiped by using acetone, ethanol, or the like, leaving onlythe substrate 41. Then, the obtained three substrates 41 are overlappedwith each other with double-sided tapes, and then punched out with aφ6.39 mm punch to prepare a sample for back ground correction(hereinafter, referred to simply as “correction sample”). After that,the M-H loop of the correction sample (substrate 41) corresponding tothe vertical direction of the substrate 41 (vertical direction of themagnetic tape MT) is measured using the VSM.

In measuring the M-H loop of the measurement sample (entire magnetictape MT) and the M-H loop of the correction sample (substrate 41), thehigh sensitivity vibrating sample magnetometer “VSM-P7-15” manufacturedby TOEI INDUSTRY CO., LTD. is used. The measurement conditions are ameasurement mode: full loop, the maximum magnetic field: 15 kOe, amagnetic field step: 40 bit, Time constant of Locking amp: 0.3 sec,Waiting time: 1 sec, and the average number of MH: 20.

After obtaining the M-H loop of the measurement sample (entire magnetictape MT) and the M-H loop of the correction sample (substrate 41),background correction is performed by subtracting the M-H loop of thecorrection sample (substrate 41) from the M-H loop of the measurementsample (entire magnetic tape MT) to obtain the M-H loop after the background correction. For the calculation of the back ground correction, ameasurement/analysis program attached to the “VSM-P7-15” is used.

A saturation magnetization Ms (emu), and a residual magnetization Mr(emu) of the obtained M-H loop after the back ground correction issubstituted into the following formula to calculate the squareness ratioS1 (%). Note that all of the above-mentioned M-H loops are measured at25° C. Further, Further, “demagnetizing field correction” when measuringthe M-H loop in the vertical direction of the magnetic tape MT is notperformed. Note that for this calculation, a measurement/analysisprogram attached to the “VSM-P7-15” is used.Squareness ratio S1(%)=(Mr/Ms)×100

A squareness ratio S2 of the magnetic layer 43 in the longitudinaldirection(travelling direction) of the magnetic tape MT is favorably 35%or less, more favorably 30% or less, still more favorably 25% or less,particularly favorably 20% or less, and most favorably 15% or less. Inthe case where the squareness ratio S2 is 35% or less, since thevertical orientation of the magnetic powder is sufficiently high,further excellent electromagnetic conversion characteristics (e.g., SNR)can be achieved.

The squareness ratio S2 in the longitudinal direction is obtained in asimilar way to the squareness ratio S1 except that the M-H loop ismeasured in the longitudinal direction (travelling direction) of themagnetic tape MT and the substrate 41.

(The Ratio Hc2/Hc1)

A ratio the ratio Hc2/Hc1 of the coercive force Hc1 of the magneticlayer 43 in the vertical direction and the coercive force Hc2 of themagnetic layer 43 in the longitudinal direction satisfies therelationship of the ratio Hc2/Hc1≤0.8, favorably the ratio Hc2/Hc1≤0.75,more favorably the ratio Hc2/Hc1≤0.7, still more favorably the ratioHc2/Hc1≤0.65, and particularly favorably the ratio Hc2/Hc1≤0.6. In thecase where the coercive forces Hc1 and Hc2 satisfy the relationship ofthe ratio Hc2/Hc1≤0.8, it is possible to increase the degree of verticalorientation of the magnetic powder. Therefore, since the magnetizationtransition width can be reduced and a high output signal can be achievedat the time of signal reproduction, it is possible to achieve furtherexcellent electromagnetic conversion characteristics (e.g., SNR). Notethat since magnetization reacts sensitively by the magnetic field in thevertical direction from the recording head in the case where Hc2 issmall as described above, it is possible to form a favorable recordingpattern.

In the case where the ratio Hc2/Hc1 satisfies the relationship of theratio Hc2/Hc1≤0.8, it is particularly effective that the averagethickness of the magnetic layer 43 is 90 nm or less. In the case wherethe average thickness of the magnetic layer 43 exceeds 90 nm, there is apossibility that the lower region (region on the side of the underlayer42) of the magnetic layer 43 is magnetized in the longitudinal directionwhen a ring-type head is used as a recording head, which makes itimpossible to uniformly magnetize the magnetic layer 43 in the thicknessdirection. Therefore, there is a possibility that further excellentelectromagnetic conversion characteristics (e.g., SNR) cannot beachieved even if the ratio Hc2/Hc1 satisfies the relationship of theratio Hc2/Hc1≤0.8 (i.e., even if the degree of vertical orientation ofthe magnetic powder is increased).

The lower limit value of the ratio Hc2/Hc1 is not particularly limited,but is, for example, 0.5 or more (0.5≤the ratio Hc2/Hc1). Note that theratio Hc2/Hc1 represents the degree of vertical orientation of themagnetic powder, and the degree of vertical orientation of the magneticpowder increases as the ratio Hc2/Hc1 is smaller.

The method of calculating the coercive force Hc2 of the magnetic layer43 in the longitudinal direction is as described above. The coerciveforce Hc1 of the magnetic layer 43 in the vertical direction is obtainedin a similar way to the coercive force Hc2 of the magnetic layer 43 inthe longitudinal direction except that the M-H loop is measured in thevertical direction (thickness direction) of the magnetic tape MT and thesubstrate 41.

(Activation Volume V_(act))

An activation volume V_(act) is favorably 8000 nm³ or less, morefavorably 6000 nm³ or less, still more favorably 5000 nm³ or less,particularly favorably 4000 nm³ or less, and most favorably 3000 nm³ orless. In the case where the activation volume V_(act) is 8000 nm³ orless, since the dispersion state of the magnetic powder is improved, thebit inversion region can be reduced, and it is possible to prevent themagnetization signal recorded in the adjacent track from beingdeteriorated due to the leakage magnetic field from the recording head.Therefore, there is a possibility that further excellent electromagneticconversion characteristics (e.g., SNR) cannot be achieved.

The above-mentioned activation volume V_(act) is obtained by thefollowing formula derived by Street&Woolley.V _(act)(nm³)=k _(B) ×T×X _(irr)/(μ₀ ×M _(S) ×S)(in which k_(B): Boltzmann's constant (1.38×10⁻²³ J/K), T: temperature(K), X_(irr): irreversible magnetic susceptibility, μ₀: vacuumpermeability, S: magnetic viscosity coefficient, Ms: saturationmagnetization (emu/cm³))

The irreversible magnetic susceptibility X_(irr), the saturationmagnetization Ms, and the magnetic viscosity coefficient S substitutedinto the above-mentioned formula are obtained as follows by using theVSM. Note that the measurement direction by the VSM is assumed to be thethickness direction (vertical direction) of the magnetic tape MT.Further, the measurement by the VSM is performed on the measurementsample cut out from the elongated magnetic tape MT at 25° C. Further,“demagnetizing field correction” when measuring the M-H loop in thethickness direction (vertical direction) of the magnetic tape MT is notperformed.

(Irreversible Magnetic Susceptibility X_(irr),)

The irreversible magnetic susceptibility X_(irr) is defined as the slopein the vicinity of a residual coercive force Hr in the slope of theresidual magnetization curve (DCD curve). First, a magnetic field of−1193 kA/m (15 kOe) is applied to the entire magnetic tape MT, and themagnetic field is returned to zero, thereby achieving a residualmagnetization state. After that, a magnetic field of approximately 15.9kA/m (200 Oe) is applied in the opposite direction, the magnetic fieldis returned to zero again, and the amount of residual magnetization ismeasured. After that, similarly, the measurement in which a magneticfield of 15.9 kA/m larger than the previous applied magnetic field isapplied and the magnetic field is returned to zero is repeated, and theamount of residual magnetization is plotted against the applied magneticfield to measure the DCD curve. A point at which the amount ofmagnetization is zero in the obtained DCD curve is taken as the residualcoercive force Hr, and the DCD curve is differentiated to obtain theslope of the DCD curve in each magnetic field. In the slope of the DCDcurve, the slope near the residual coercive force Hr is X_(irr).

(Saturation Magnetization Ms)

First, in a similar way to the above-mentioned method of measuring thesquareness ratio S1, the M-H loop after background correction isobtained. Next, on the basis of the value of the saturationmagnetization Ms (emu) of the obtained M-H loop and the volume (cm³) ofthe magnetic layer 43 in the measurement sample, Ms (emu/cm³) iscalculated. Note that the volume of the magnetic layer 43 is obtained bymultiplying the area of the measurement sample by the average thicknessof the magnetic layer 43. The method of calculating the averagethickness of the magnetic layer 43 necessary for calculating the volumeof the magnetic layer 43 is as described above.

(Magnetic Viscosity Coefficient S)

First, a magnetic field of −1193 kA/m (15 kOe) is applied to the entiremagnetic tape MT (measurement sample), and the magnetic field isreturned to zero, thereby achieving a residual magnetization state.After that, a magnetic field having a value similar to that of theresidual coercive force Hr obtained from the DCD curve is applied in theopposite direction. In the state where the magnetic field is applied,the amount of magnetization is continuously measured at constant timeintervals for 1000 seconds. The relationship between a time t and amagnetization amount M(t) thus obtained is compared with the followingformula to calculate the magnetic viscosity coefficient S.M(t)=M0+S×ln(t)(in which M(t): a magnetization amount at the time t, M0: an initialmagnetization amount, S: a magnetic viscosity coefficient, ln(t): anatural logarithm of time)

(Surface Roughness R_(b) of Back Surface)

It is favorable that a surface roughness R_(b) of a back surface(surface roughness of the back layer 44) satisfies the relationship ofR_(b)≤6.0 [nm]. In the case where the surface roughness R_(b) of theback surface is within the above-mentioned range, further excellentelectromagnetic conversion characteristics can be achieved.

The surface roughness R_(b) of the back surface is obtained as follows.First, the magnetic tape MT having width of 12.65 mm is prepared and cutinto a 100 mm length to prepare a sample. Next, the sample is placed ona slide glass so that a surface of the sample to be measured (surface onthe magnetic layer side) is directed upward, and an end of the sample isfixed with a mending tape. The surface shape is measured using VertScan(objective lens 50 times) as a measurement apparatus, and the surfaceroughness R_(b) of the back surface is obtained from the followingformula on the basis of the ISO 25178 standard.

Apparatus: Non-contact roughness meter using optical interference(manufactured by Ryoka Systems Inc., non-contact surface/layercross-sectional shape measurement system VertScan R5500GL-M100-AC)

Objective lens: 20 times

Measurement region: 640×480 pixels (field of view: approximately 237μm×178 μm field of view)

Measurement mode: phase

Wavelength filter: 520 nm

CCD:⅓ lens

Noise removal filter: smoothing 3×3

Surface correction: correction on quadratic polynomial approximatedsurface

Measurement software: VS-Measure Version5.5.2

Analysis software: VS-viewer Version5.5.5

$\begin{matrix}{S_{a} = {\frac{1}{A}{\int_{A}{\int{{{Z\left( {x,y} \right)}}{dxdy}}}}}} & \left( {{Math}.\mspace{14mu} 8} \right)\end{matrix}$

After measuring the surface roughness at least five or more points inthe longitudinal direction as described above,

the average value of arithmetic average roughnesses Sa (nm)automatically calculated on the basis of the surface profile obtained ateach position is taken as the surface roughness R_(b) (nm) of the backsurface.

(Young's Modulus of Magnetic Tape in Longitudinal Direction)

The Young's modulus of the magnetic tape MT in the longitudinaldirection is favorably 8.0 GPa or less, more favorably 7.9 GPa or less,still more favorably 7.5 GPa or less, and particularly favorably 7.1 GPaor less. In the case where the Young's modulus of the magnetic tape MTin the longitudinal direction is 8.0 GPa or less, theexpansion/contraction property of the magnetic tape MT due to anexternal force is further enhanced, which makes it easier to adjust thewidth of the magnetic tape MT by tension adjustment. Therefore, it ispossible to further appropriately suppress off-track and furtheraccurately reproduce data recorded in the magnetic tape MT.

The Young's modulus of the magnetic tape MT in the longitudinaldirection is a value indicating the difficulty of expansion andcontraction of the magnetic tape MT in the longitudinal direction due toan external force. The larger this value, the more difficult themagnetic tape MT is expanded and contracted in the longitudinaldirection due to an external force. The smaller this value, the easierthe magnetic tape MT is expanded and contracted in the longitudinaldirection due to an external force.

Note that the Young's modulus of the magnetic tape MT in thelongitudinal direction is a value relating to the magnetic tape MT inthe longitudinal direction, and is correlated with the difficulty ofexpansion and contraction of the magnetic tape MT in the widthdirection. That is, the larger this value, the more difficult themagnetic tape MT is expanded and contracted in the width direction dueto an external force. The smaller this value, the easier the magnetictape MT is expanded and contracted in the width direction due to anexternal force. Therefore, from the viewpoint of tension adjustment, itis advantageous that the Young's modulus of the magnetic tape MT in thelongitudinal direction is smaller.

For measurement of the Young's modulus, a tensile tester (manufacturedby Shimadzu Corporation, AG-100D) is used. In the case where the Young'smodulus in the tape longitudinal direction is desired to be measured,the tape is cut into a 180 mm length to prepare a measurement sample. Ajig capable of fixing the tape width (½ inch) is attached to theabove-mentioned tensile tester to fix the top and bottom of the tapewidth. The distance (length of the tape between chucks) is set to 100mm. After chucking the data sample, stress is gradually applied in thedirection of pulling the sample. The pulling speed is set to 0.1 mm/min.The Young's modulus is calculated using the following formula on thebasis of the change in stress and the amount of elongation at this time.E(N/m ²)=((ΔN/S)/(Δx/L))×10⁶

ΔN: change in stress (N)

S: cross-sectional area of test piece (mm₂)

Δx: amount of elongation (mm)

L: distance between gripping jigs (mm)

The stress range is 0.5N to 1.0N, and the change in stress (ΔN) and theamount of elongation (Δx) at this time are used for calculation.

(Young's Modulus of Substrate in Longitudinal Direction)

The Young's modulus of the substrate 41 in the longitudinal direction isfavorably 7.5 GPa or less, more favorably 7.4 GPa or less, still morefavorably 7.0 GPa or less, and particularly favorably 6.6 GPa or less.In the case where the Young's modulus of the substrate 41 in thelongitudinal direction is 7.5 GPa or less, the expansion/contractionproperty of the magnetic tape MT due to an external force is furtherenhanced, which makes it easier to adjust the width of the magnetic tapeMT by tension adjustment. Therefore, it is possible to furtherappropriately suppress off-track and further accurately reproduce datarecorded in the magnetic tape MT.

The above-mentioned Young's modulus of the substrate 41 in thelongitudinal direction is obtained as follows. First, the underlayer 42,the magnetic layer 43, and the back layer 44 are removed from themagnetic tape MT to obtain the substrate 41. Using this substrate 41,the Young's modulus of the substrate 41 in the longitudinal direction isobtained in a similar procedure to the above-mentioned Young's modulusof the magnetic tape MT in the longitudinal direction.

The thickness of the substrate 41 is more than half the thickness of theentire magnetic tape MT. Therefore, the Young's modulus of the substrate41 in the longitudinal direction is correlated with the difficulty ofexpansion and contraction of the magnetic tape MT due to an externalforce. The larger this value, the more difficult the magnetic tape MT isexpanded and contracted in the width direction due to an external force.The smaller this value, the easier the magnetic tape MT is expanded andcontracted in the width direction due to an external force.

Note that the Young's modulus of the substrate 41 in the longitudinaldirection is a value relating to the magnetic tape MT in thelongitudinal direction, and is correlated with the difficulty ofexpansion and contraction of the magnetic tape MT in the widthdirection. That is, the larger this value, the more difficult themagnetic tape MT is expanded and contracted in the width direction dueto an external force. The smaller this value, the easier the magnetictape MT is expanded and contracted in the width direction due to anexternal force. Therefore, from the viewpoint of tension adjustment, itis advantageous that the Young's modulus of the substrate 41 in thelongitudinal direction is smaller.

(Dynamic Friction Coefficient)

A friction coefficient ratio (μ_(B)/μ_(A)) of a dynamic frictioncoefficient μ_(B) between the surface of the magnetic layer 43 and themagnetic head 56 when the tension applied to the magnetic tape MT is 0.4N to a dynamic friction coefficient μ_(A) between the surface of themagnetic layer 43 and the magnetic head 56 when the tension applied tothe magnetic tape MT is 1.2 N is favorably 1.0 or more and 2.0 or less,more favorably 1.0 or more and 1.5 or less. In the case where thefriction coefficient ratio (μ_(B)/μ_(A)) is 1.0 or more an 2.0 or less,the change in the dynamic friction coefficient due to tensionfluctuation during travelling can be reduced, and thus, excellenttravelling stability can be achieved also in the case where tensionadjustment of the magnetic tape MT is performed during travelling of themagnetic tape MT.

The dynamic friction coefficient μ_(A) and the dynamic frictioncoefficient μ_(B) for calculating the friction coefficient ratio(μ_(B)/μ_(A)) are obtained as follows. First, as shown in Part A of FIG.10 , the magnetic tape MT having a width of ½ inch is placed on twoguide rolls 73A and 73B each having a cylindrical shape having adiameter of one inch disposed in parallel to be apart from each other sothat the magnetic surface is in contact with the guide rolls 73A and73B. The two the guide rolls 73A and 73B are fixed to a hard platemember 76, and thus, the positional relationship between them is fixed.

Subsequently, the magnetic tape MT is caused to be in contact with ahead block (for recording/reproduction) 74 mounted on the LTOS drive sothat the magnetic surface is in contact with the head block 74 and awrap angle θ₁ (°)=5.6°. The head block 74 is disposed substantially atthe center of the guide rolls 73A and 73B. The head block 74 is movablyattached to the plate member 76 so that the wrap angel θ₁ can bechanged. However, in the case where the wrap angle θ₁ (°) becomes 5.6°,the position is fixed to the plate member 76, thereby fixing also thepositional relationship between the guide rolls 73A and 73B and the headblock 74.

One end of the magnetic tape MT is connected to a movable strain gauge71 via a jig 72. As shown in Part B of FIG. 10 , the magnetic tape MT isfixed to the jig 72. A weight 75 is connected to the other end of themagnetic tape MT. The weight 75 applies tension of 0.4 N (T₀[N]) in thelongitudinal direction of the magnetic tape MT. The movable strain gauge71 is fixed on a base 77. Also the positional relationship between thebase 77 and the plate member 76 is fixed, and thus, the positionalrelationship between the guide rolls 73A and 73B, the head block 74, andthe movable strain gauge 71 is fixed.

The movable strain gauge 71 slides the magnetic tape MT on the headblock 74 by 60 mm so that the magnetic tape MT moves to the movablestrain gauge 71 at 10 mm/s. The output value (voltage) of the movablestrain gauge 71 during sliding is converted into T[N] on the basis ofthe linear relationship (described below) between the output value andthe load acquired in advance. T[N] is acquired 13 times during theperiod from the start to stop of the above-mentioned 60 mm sliding, and11 T[N] excluding the first one and the last one are simply averaged,thereby obtaining T_(ave) [N].

After that, the dynamic friction coefficient μ_(A) is obtained using thefollowing formula.

$\begin{matrix}{\mu_{A} = {\frac{1}{\left( {\theta_{1}\lbrack{^\circ}\rbrack} \right) \times \left( {\pi/180} \right)} \times {\ln\left( \frac{T_{ave}\lbrack N\rbrack}{T_{0}\lbrack N\rbrack} \right)}}} & \left( {{Math}.\mspace{14mu} 9} \right)\end{matrix}$

The above-mentioned linear relationship is obtained as follows. That is,the output values (voltage) of the movable strain gauge 71 both in thecase where a load of 0.4 N is applied to the movable strain gauge 71 andin the case where a load of 1.5 N is applied to the movable strain gauge71 are obtained. The linear relationship between the output value andthe load is obtained on the basis of the two obtained output values andthe above-mentioned two loads. Using the linear relationship, the outputvalue (voltage) of the movable strain gauge 71 during sliding isconverted into T[N] as described above.

The dynamic friction coefficient μ_(B) is measured by the same method asthe method of measuring the dynamic friction coefficient μ_(A) exceptthat the above-mentioned tension T₀[N] to be applied to the other end isset to 1.2 N.

On the basis of the dynamic friction coefficient μ_(A) and the dynamicfriction coefficient μ_(B) measured in this way, the frictioncoefficient ratio (μB/μA) is calculated.

When the dynamic friction coefficient between the surface of themagnetic layer 43 and the magnetic head 56 in the case where tension tobe applied to the magnetic tape MT is 0.6 N is μ_(C), the frictioncoefficient ratio (μ_(C)(1000)/μ_(C)(5)) of the dynamic frictioncoefficient μ_(C) (1000) at the time of 1000th travelling to the dynamicfriction coefficient μ_(C) (5) at the time of fifth travelling isfavorably 1.0 or more and 2.0 or less, more favorably 1.0 or more and1.5 or less. In the case where the friction coefficient ratio(μ_(C)(1000)/μ_(C)(5)) is 1.0 or more and 2.0 or less, the change in thedynamic friction coefficient after the 1000th travelling can be reduced,and thus, excellent travelling stability can be achieved even after the1000th travelling. Here, as the magnetic head 56, one including a drivethat supports the magnetic tape MT is used.

The dynamic friction coefficient μ_(C)(5) and the dynamic frictioncoefficient μ_(C)(1000) for calculating the friction coefficient ratio(μ_(C)(1000)/μ_(C)(5)) are obtained as follows. The magnetic tape MT isconnected to the movable strain gauge 71 in the same way as the methodof measuring the dynamic friction coefficient μA except that theabove-mentioned tension T₀[N] to be applied to the other end of themagnetic tape MT is set to 0.6 N. Then, the magnetic tape MT is slid by60 mm toward the movable strain gauge at 10 mm/s with respect to thehead block 74 (outward path), and slid by 60 mm to be away from themovable strain gauge (return path). This reciprocating operation isrepeated 1000 times. The output value (voltage) of the movable straingauge is acquired 13 times during the period from the start of the fifth60 mm sliding through the outward path to the stop of sliding in the1000 reciprocating operations, and is converted into T[N] on the basisof the linear relationship (described below) between the output valueand the load obtained in the dynamic friction coefficient μ_(A). ElevenT[N] excluding the first one and the last one are simply averaged,thereby obtaining T_(ave) [N]. The dynamic friction coefficient μ_(C)(5)is obtained using the following formula.

$\begin{matrix}{{\mu_{C}(5)} = {\frac{1}{\left( {\theta_{1}\lbrack{^\circ}\rbrack} \right) \times \left( {\pi/180} \right)} \times {\ln\left( \frac{T_{ave}\lbrack N\rbrack}{T_{0}\lbrack N\rbrack} \right)}}} & \left( {{Math}.\mspace{14mu} 10} \right)\end{matrix}$

The above-mentioned linear relationship is obtained as follows. That is,the output values (voltage) of the movable strain gauge 71 both in thecase where a load of 0.4 N is applied to the movable strain gauge 71 andin the case where a load of 1.5 N is applied to the movable strain gauge71 are obtained. The linear relationship between the output value andthe load is obtained on the basis of the two obtained output values andthe above-mentioned two loads. Using the linear relationship, the outputvalue (voltage) of the movable strain gauge 71 during sliding isconverted into T[N] as described above.

Further, the dynamic friction coefficient μ_(C)(1000) is obtained in asimilar way to the dynamic friction coefficient μ_(C)(5) except thatmeasurement on the 1000th outward path is performed.

On the basis of the dynamic friction coefficient μ_(C)(5), and thedynamic friction coefficient μ_(C)(1000) measured as described above,the friction coefficient ratio μ_(C)(1000)/μ_(C)(5) is calculated.

[Configuration of Servo Writer]

Next, an example of a configuration of a servo writer 210 to be used forwriting the above-mentioned servo pattern will be described withreference to FIG. 11 , Part A of FIG. 12 , and Part B of FIG. 12 .

The servo writer 210 has a configuration similar to that of the servowriter described in WO 2019/093469 (particularly, servo writer describedwith reference to FIG. 1 in the same literature) except for a servosignal writing head 219. As the servo signal writing head 219, the servosignal writing head described in Japanese Patent Application Laid-openNo. 2006-127730 (particularly, the servo signal writing head describedwith reference to FIG. 26 in the same literature).

As shown in FIG. 11 , a servo track writer 210 includes a delivery reel211, a take-up reel 212, capstans 213A and 214A, pinch rollers 213B and214B, guide rollers 215A and 215B, a polishing unit 216, a dusting unit217, a tension adjustment unit 218, the servo signal writing head 219, aservo signal reading head 220, a preamplifier 221, a control device 222,a pulse generation circuit 223, and a drive device 224. This servo trackwriter 210 is an apparatus for writing a servo signal to servo bands ofthe elongated magnetic tape MT. The tension adjustment unit 218 includesa tension arm 218A and a pair of support units 218B.

As shown in Part A of FIG. 12 , the servo signal writing head 219includes a head chip 232, and has, on the top surface of the head chip232, a sliding surface 234 for a linear-type magnetic tape (not shown).In the sliding surface 234, at least a magnetic head unit 235 includingrecording elements, some of which is used for servo signal recording,and a bottomed cavity 236 having a closed periphery are formed.

As shown in Part B of FIG. 12 , at least a part of the sliding surface234 of the servo signal writing head 219 is a flat surface. Alinear-type magnetic tape (not shown) disposed to face the slidingsurface 234 has a smaller spacing with the sliding surface 234 duringtravelling, because the nearby air is taken by the edge portion of themagnetic head sliding surface 234 and the pressure is reduced by thebottomed cavity 236.

By adjusting the distance between the servo signal writing head 219,which is mounted on the servo track writer 210 and has a cavity, and theguide rollers 215A and 215B adjacent to the servo signal writing head219, and adjusting the angle of the tape entering the servo signalwriting head 219, it is possible to adjust the friction between theservo signal writing head 219 and the magnetic tape MT when recordingservo patterns. By adjusting the friction in this way, it is possible toadjust σ_(SW) of the magnetic tape MT. As the friction between the servosignal writing head 219 and the magnetic tape MT when recording servopatterns is reduced, σ_(SW) tends to decrease.

[Method of Producing Magnetic Tape]

Next, an example of the method of producing the magnetic tape MT havingthe above-mentioned configuration will be described.

(Process of Preparing Coating Material)

First, a non-magnetic powder, a binder, and the like are kneaded anddispersed in a solvent to prepare a coating material for forming anunderlayer. Next, a magnetic powder, a binder, and the like are kneadedand dispersed in a solvent to prepare a coating material for forming amagnetic layer. For the preparation of the coating material for forminga magnetic layer and the coating material for forming an underlayer, forexample, the following solvents, dispersing devices, and kneadingdevices can be used.

Examples of the solvent used for preparing the above-mentioned coatingmaterial include ketone solvents such as acetone, methyl ethyl ketone,methyl isobutyl ketone, and cyclohexanone, alcohol solvents such asmethanol, ethanol, and propanol, ester solvents such as methyl acetate,ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, andethylene glycol acetate, ether solvents such as diethylene glycoldimethyl ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane, aromatichydrocarbon solvents such as benzene, toluene, and xylene, andhalogenated hydrocarbon solvents such as methylene chloride, ethylenechloride, carbon tetrachloride, chloroform, and chlorobenzene. These maybe used alone or mixed appropriately for use.

As the kneading device used for preparing the above-mentioned coatingmaterial, for example, kneading devices such as a continuous twin-screwkneader, a continuous twin-screw kneader capable of performing dilutionin multi-stages, a kneader, a pressure kneader, and a roll kneader canbe used. However, the present disclosure is not particularly limited tothese devices. Further, as the dispersing device used for preparing theabove-mentioned coating material, for example, dispersing devices suchas a roll mill, a ball mill, a horizontal sand mill, a vertical sandmill, a spike mill, a pin mill, a tower mill, a pearl mill (e.g., “DCPmill” manufactured by Nippon Eirich Co., Ltd.) a homogenizer, and anultrasonic dispersion machine can be used. However, the presentdisclosure is not particularly limited to these devices.

(Coating Process)

Next, the coating material for forming an underlayer is coated on onemain surface of the substrate 41 and dried to form the underlayer 42.Subsequently, the coating material for forming a magnetic layer iscoated on the underlayer 42 and dried to form the recording layer 43 onthe underlayer 42. Note that during drying, the magnetic field of themagnetic powder may be oriented in the thickness direction of thesubstrate 41 by, for example, a solenoid coil. Further, during drying,after the magnetic field of the magnetic powder may be oriented in thetravelling direction (longitudinal direction) of the substrate 41 by,for example, a solenoid coil, the magnetic field of the magnetic powdermay be oriented in the thickness direction of the substrate 41. Byperforming processing of causing the magnetic field of the magneticpowder to be oriented in the longitudinal direction as described above,it is possible to further improve the degree of vertical orientation(i.e., the squareness ratio S1) of the magnetic powder. After formingthe magnetic layer 43, the back layer 44 is formed on the other mainsurface of the substrate 41. As a result, the magnetic tape MT isobtained.

The squareness ratios S1 and S2 are each set to a desired value byadjusting, for example, the strength of the magnetic field to be appliedto the coating film of the coating material for forming a magneticlayer, the concentration of solid content in the coating material forforming a magnetic layer, and the drying conditions (drying temperatureand drying time) of the coating film of the coating material for forminga magnetic layer. The strength of the magnetic field to be applied tothe coating film is favorably two or more times and three or less timesthe coercive force of the magnetic powder. In order to further increasethe squareness ratio S1 (i.e., in order to further decrease thesquareness ratio S2), it is favorable to improve the dispersion state ofthe magnetic powder in the coating material for forming a magneticlayer. Further, in order to further increase the squareness ratio S1, itis also effective to magnetize the magnetic powder at the stage beforethe coating material for forming a magnetic layer enters the orientationdevice for causing the magnetic field of the magnetic powder to beoriented. Note that the above-mentioned method of adjusting thesquareness ratios S1 and S2 may be used alone or two or more methods maybe used in combination.

(Calendar Process and Transfer Process)

After that, calendar process is performed on the obtained magnetic tapeMT to smooth the surface of the magnetic layer 43. Next, after winding,into a roll, the magnetic tape MT on which calendar process has beenperformed, heat treatment is performed on the magnetic tape MT in thisstate, and thus, the protrusions 44A on the surface of the back layer 44are transferred to the surface of the magnetic layer 43. As a result,the holes 43A are formed on the surface of the magnetic layer 43.

The temperature of the heat treatment is favorably 55° C. or more and75° C. or less. In the case where the temperature of the heat treatmentis 55° C. or more, favorable transferability can be achieved. Meanwhile,if the temperature of the heat treatment exceeds 75° C., there is apossibility that the amount of pores is too much and the lubricant onthe surface of the magnetic layer 43 is excessive. Here, the temperatureof the heat treatment is a temperature of an atmosphere for holding themagnetic tape MT.

The time for the heat treatment is favorably 15 hours or more and 40hours or less. In the case where the time for the heat treatment is 15or more, favorable transferability can be achieved. Meanwhile, in thecase where the time for the heat treatment is 40 hours or less, it ispossible to suppress the decrease in productivity.

(Cut Process)

Finally, the magnetic tape MT is cut into a predetermined width (e.g., ½inch width). The magnetic tape MT is obtained in this way.

(Process of Writing Servo Pattern)

The above-mentioned servo writer 210 writes servo patterns to themagnetic tape MT. At this time, by adjusting the friction between theservo signal writing head 119 and the magnetic tape MT when writingservo patterns as described above, the statistical value σ_(SW) of themagnetic tape MT can be adjusted to 24 nm or less.

[Configuration of Recording/Reproduction Apparatus]

The recording/reproduction apparatus 50 performs recording andreproduction of the magnetic tape MT having the above-mentionedconfiguration. The recording/reproduction apparatus 50 has aconfiguration in which tension to be applied to the longitudinaldirection of the magnetic tape MT can be adjusted. Further, therecording/reproduction apparatus 50 has a configuration in which thecartridge 10 can be loaded. Here, in order to facilitate thedescription, a case where the recording/reproduction apparatus 50 has aconfiguration in which one cartridge 10 can be loaded will be described.However, the recording/reproduction apparatus 50 may have aconfiguration in which a plurality of cartridges 10 can be loaded.

The recording/reproduction apparatus 50 is connected to informationprocessing apparatuses such as a server 61 and a personal computer(hereinafter, referred to as “PC”) 62 via a network 60, and configuredto be capable of recording, in the cartridge 10, data supplied fromthese information processing apparatuses. Further, therecording/reproduction apparatus 50 is configured to be capable ofreproducing the data from the cartridge 10 and supplying the data to theinformation processing apparatuses, in response to a request from theinformation processing apparatuses. The shortest recording wavelength ofthe recording/reproduction apparatus 50 is favorably 96 nm or less, morefavorably 88 nm or less, and still more favorably 80 nm or less.

As shown in FIG. 1 , the recording/reproduction apparatus 50 includes aspindle 51, a reel 52 on the side of the recording/reproductionapparatus 50, a spindle drive device 53, a reel drive device 54, aplurality of guide rollers 55, a magnetic head (head unit) 56, thereader/writer 57 as a communication unit, a communication interface(hereinafter, I/F) 58, and the control device 59.

The spindle 51 is configured to be capable of mounting the cartridge 10.In the magnetic tape MT, a servo pattern having an inverted V shape isrecorded as a servo signal in advance. The reel 52 is configured to becapable of fixing the tip (leader pin 20) of the magnetic tape MT pulledout of the cartridge 10 via a tape loading mechanism (not shown).

The spindle drive device 53 rotates the spindle 51 in response to acommand from a control device 59. The reel drive device 54 rotates thereel 52 in response to a command from the control device 59. Theplurality of guide rollers 55 guides the travelling of the magnetic tapeMT so that the tape path formed between the cartridge 10 and the reel 52has a predetermined relative positional relationship with the magnetichead 56.

When recording data on the magnetic tape MT or reproducing data from themagnetic tape MT, the spindle drive device 53 and the reel drive device54 respectively drive the spindle 51 and the reel 52 to rotate, and themagnetic tape MT travels. The magnetic tape MT can be reciprocated inthe travelling direction of the forward direction (direction flowingfrom the cartridge 10 side to the reel 52 side) and the reversedirection (direction flowing from the reel 52 side to the cartridge 10side).

In this embodiment, the tension of the magnetic tape MT in thelongitudinal direction during data recording or data reproduction can beadjusted by control of rotation of the spindle 51 by the spindle drivedevice 53 and control of rotation of the reel 52 by the reel drivedevice 54. Note that the tension adjustment of the magnetic tape MT maybe performed by control of movement of the guide rollers 55 instead ofor in addition to the control of rotation of the spindle 51 and the reel52.

The reader/writer 57 is configured to be capable of writing the firstinformation and the second information to the cartridge memory 11 inresponse to a command from the control device 59. Further, thereader/writer 57 is configured to be capable of reading the firstinformation and the second information from the cartridge memory 11 inresponse to a command from the control device 59. As the communicationmethod between the reader/writer 57 and the cartridge memory 11, forexample, the ISO14443 is adopted. The second information includestension adjustment information. The tension adjustment information is anexample of information during data recording.

The control device 59 includes, for example, a control unit, a storageunit, a communication unit, and the like. The control unit includes, forexample, a CPU (Central Processing Unit), and controls the respectiveunits of the recording/reproduction apparatus 50 in accordance with theprogram stored in the storage unit. For example, in response to arequest from the information processing apparatus such as the server 61and the PC 62, the control device 59 records, in the magnetic tape MT bythe magnetic head 56, the data signal supplied from the informationprocessing apparatus. Further, in response to a request from theinformation processing apparatus such as the server 61 and the PC 62,the control device 59 reproduces the data signal recorded in themagnetic tape MT and supplies the data signal to the informationprocessing apparatus, by the magnetic head 56.

The storage unit includes a non-volatile memory in which various typesof data and various programs are recorded, and a volatile memory to beused as a work area of the control unit. The above-mentioned variousprograms may be read from a portable recording medium such as an opticaldisk or a portable storage device such as a semiconductor memory, ordownloaded from a server apparatus on a network.

The control device 59 reads the servo signal recorded on two adjacentservo bands SB by the magnetic head 56 during data recording on themagnetic tape MT or data reproduction from the magnetic tape MT. Thecontrol device 59 uses the servo signal read from the two servo bands SBto control the position of the magnetic head 56 so that the magnetichead 56 follows the servo pattern.

The control device 59 obtains a distance (distance in the widthdirection of the magnetic tape MT) d1 between two adjacent servo bandsSB from the reproduction waveform of the servo signal read from the twoadjacent servo bands SB during data recording on the magnetic tape MT.Then, the control device 59 writes the obtained distance to the memory36 by the reader/writer 57.

The control device 59 obtains a distance (distance in the widthdirection of the magnetic tape MT) d2 between two adjacent servo bandsSB from the reproduction waveform of the servo signal read from the twoadjacent servo bands SB during data reproduction from the magnetic tapeMT. In addition thereto, the control device 59 reads, from the memory 36by the reader/writer 57, the distance d1 between the two adjacent servobands SB obtained during data recording on the magnetic tape MT. Thecontrol device 59 controls the rotation of the spindle drive device 53and the reel drive device 54 so that a difference Δd between thedistance d1 between the servo bands SB obtained during the datarecording on the magnetic tape MT and the distance d2 between the servobands SB obtained during data reproduction from the magnetic tape MT iswithin a specified range, thereby adjusting the tension to be applied inthe longitudinal direction of the magnetic tape MT. The control of thistension adjustment is performed by, for example, feedback control.

The magnetic head 56 is configured to be capable of recording data onthe magnetic tape MT in response to a command from the control device59. Further, the magnetic head 56 is configured to be capable ofreproducing, in response to a command from the control device 59, datarecorded in the magnetic tape MT. The magnetic head 56 includes, forexample, the two servo lead heads 56A and 56B, a plurality of datawrite/read heads, and the like.

The servo lead heads 56A and 56B are each configured to be capable ofreading the magnetic field generated from the servo signal recorded inthe magnetic tape MT by an MR (Magneto Resistive) device or the like toreproduce the servo signal. The interval between the two servo leadheads 56A and 56B in the width direction is substantially the same asthe distance between the two adjacent servo bands SB.

The data write/read heads are arranged at positions sandwiched betweenthe two servo lead heads 56A and 56B along the direction from one of theservo lead heads 56A and 56B toward the other at equal intervals. Thedata write/read heads are each configured to be capable of recordingdata on the magnetic tape MT by the magnetic field generated from themagnetic gap. Further, the data write/read heads are each configured tobe capable of reading, by the MR device or the like, the magnetic fieldgenerated from the data recorded in the magnetic tape MT to reproducethe data.

The communication I/F 58 is for communicating with the informationprocessing apparatus such as the server 61 and the PC 62, and isconnected to the network 60.

[Operation of Recording/Reproduction Apparatus During Data Recording]

Hereinafter, an example of the operation of the recording/reproductionapparatus 50 during data recording will be described with reference toFIG. 13 .

First, the control device 59 loads the cartridge 10 into therecording/reproduction apparatus 50 (Step S11). Next, the control device59 controls rotation of the spindle 51 and the reel 52, and causes themagnetic tape MT to travel while applying specified tension in thelongitudinal direction of the magnetic tape MT. Then, the control device59 reads the servo signal by the servo lead heads 56A and 56B of themagnetic head 56, and records data on the magnetic tape MT by the datawrite/read head of the magnetic head 56 (Step S12).

At this time, the magnetic head 56 records data on the data band DB bythe data write/read head of the magnetic head 56 while tracing twoadjacent servo bands SB by the two servo lead heads 56A and 56B of themagnetic head 56.

Next, the control device 59 obtains the distance d1 between the twoadjacent servo bands SB during data recording from the reproductionwaveform of the servo signal read by the servo lead heads 56A and 56B ofthe magnetic head 56 (Step S13). Next, the control device 59 writes thedistance d1 between the servo bands SB during data recording to thecartridge memory 11 by the reader/writer 57 (Step S14). The controldevice 59 may continuously measure the distance d1 between the servobands SB and write the distance D1 to the cartridge memory 11.Alternatively, the control device 59 may measure the distance d1 betweenthe servo bands at regular intervals, and write the distance d1 to thecartridge memory 11. In the case of measuring the distance d1 betweenthe servo bands SB at regular intervals and writing the distance d1 tothe cartridge memory 11, it is possible to reduce the amount ofinformation to be written to the memory 36.

[Operation of Recording/Reproduction Apparatus During Data Reproduction]

Hereinafter, an example of the operation of the recording/reproductionapparatus 50 during data reproduction will be described with referenceto FIG. 14 .

First, the control device 59 loads the cartridge 10 into therecording/reproduction apparatus 50 (Step S21). Next, the control device59 reads the distance d1 between the servo bands during recording fromthe cartridge memory 11 by the reader/writer 57 (Step S22).

Next, the control device 59 controls rotation of the spindle 51 and thereel 52, and causes the magnetic tape MT to travel while applyingspecified tension in the longitudinal direction of the magnetic tape MT.Then, the control device 59 reads the servo signal by the servo leadheads 56A and 56B of the magnetic head 56, and reproduces the data fromthe magnetic tape MT by the data write/read head of the magnetic head 56(Step S23).

Next, the control device 59 calculates the distance d2 between the twoadjacent servo bands SB during data reproduction from the reproductionwaveform of the servo signal read by the servo lead heads 56A and 56B ofthe magnetic head 56 (Step S24).

Next, the control device 59 determines whether or not the difference Δdbetween the distance d1 between the servo bands read in Step S22 and thedistance d2 between the servo bands SB calculated in Step S24 is withina specified value (Step S25).

In the case where it is determined in Step S25 that the difference Δd iswithin the specified value, the control device 59 controls rotation ofthe spindle 51 and the reel 52 so that specified tension is maintained(Step S26).

Meanwhile, in the case where it is determined in Step S25 that thedifference Δd is not within the specified value, the control device 59controls rotation of the spindle 51 and the reel 52 so that thedifference Δd is decreased to adjust tension to be applied to thetravelling magnetic tape MT, and the processing returns to Step S24(Step S27).

[Effect]

As described above, in the magnetic tape MT according to the firstembodiment, since the BET specific surface area of the entire magnetictape MT measured in the state where the magnetic tape MT has been washedand dried is 3.5 m²/g or more and 7.0 m²/g or less and the statisticalvalue σ_(SW) indicating the non-linearity of the servo pattern is 24 nm,excellent travelling stability can be achieved even in the case wherethe total thickness of the magnetic tape MT is small. Further, since thearithmetic average roughness Ra of the surface of the magnetic layer 43is 2.5 nm or less, the squareness ratio of the magnetic layer 43 in thevertical direction is 65%, and the average thickness of the magneticlayer 43 is 80 nm, excellent electromagnetic conversion characteristicscan be achieved. Therefore, it is possible to achieve both excellenttravelling stability and the electromagnetic conversion characteristics.

Further, in the magnetic tape MT according to the first embodiment, thesubstrate 41 includes polyester. As a result, in the case where thewidth of the magnetic tape MT changes due to changes in the ambienttemperature or humidity around the magnetic tape MT (cartridge 10) inwhich data is recorded with the above-mentioned data track width, it ispossible to keep the width of the magnetic tape MT constant orsubstantially constant by adjusting, by the recording/reproductionapparatus 50, the tension of the magnetic tape MT in the longitudinaldirection during travelling. Therefore, it is possible to suppressoff-track caused by changes in the ambient temperature or humidity.

2 Second Embodiment

[Configuration of Recording/Reproduction Apparatus]

FIG. 15 is a schematic diagram showing an example of a configuration ofa recording/reproduction system 100A according to a second embodiment ofthe present disclosure. The recording/reproduction system 100A includesthe cartridge 10 and the recording/reproduction apparatus 50A.

The recording/reproduction apparatus 50A further includes a thermometer63 and a hygrometer 64. The thermometer 63 measures the temperaturearound the magnetic tape MT (cartridge 10) and outputs the temperatureto the control device 59. Further, the hygrometer 64 measures thehumidity around the magnetic tape MT (cartridge 10) and outputs thehumidity to the control device 59.

The control device 59 measures, by the thermometer 63 and the hygrometer64 a temperature Tm1 and a humidity H1 around the magnetic tape MT(cartridge 10) during data recording on the magnetic tape MT, and writesthem to the cartridge memory 11 via the reader/writer 57. Each of thetemperature Tm1 and the humidity H1 is an example of informationregarding the environment around the magnetic tape MT.

The control device 59 obtains, on the basis of drive data of the spindle51 and the reel 52, a tension Tn1 that has been applied in thelongitudinal direction of the magnetic tape MT during data recording onthe magnetic tape MT, and writes the tension Tn1 to the cartridge memory11 via the reader/writer 57.

The control device 59 obtains, on the basis of the reproduction waveformof the servo signal read from two adjacent servo bands SB, the distanced1 between the two adjacent servo bands SB during data recording on themagnetic tape MT. Then, the control device 59 calculates, on the basisof the distance d1, a width W1 of the magnetic tape MT during datarecording, and writes the width W1 to the memory 36 by the reader/writer57.

The control device 59 measures, by the thermometer 63 and the hygrometer64, a temperature Tm2 and a humidity H2 around the magnetic tape MT(cartridge 10) during data reproduction from the magnetic tape MT.

The control device 59 obtains, on the basis of drive data of the spindle51 and the reel 52, a tension Tn2 that has been applied in thelongitudinal direction of the magnetic tape MT during data reproductionfrom the magnetic tape MT.

The control device 59 obtains, on the basis of the reproduction waveformof the servo signal read from two adjacent servo bands SB, the distanced2 between the two adjacent servo bands SB during data reproduction fromthe magnetic tape MT. Then, the control device 59 calculates, on thebasis of the distance d2, a width W2 of the magnetic tape MT during datareproduction.

The control device 59 reads, during data reproduction from the magnetictape MT, the temperature Tm1, the humidity H1, the tension Tn1, and thewidth W1 that have been written during data recording from the cartridgememory 11 via the reader/writer 57. Then, the control device 59 uses thetemperature Tm1, the humidity H1, the tension Tn1, and the width W1during data recording and the temperature Tm2, the humidity H2, thetension Tn2, and the width W2 during data reproduction to controltension to be applied to the magnetic tape MT so that the width W2 ofthe magnetic tape MT during data reproduction is equal to orsubstantially equal to the width W1 of the magnetic tape during datarecording.

The controller 35 of the cartridge memory 11 stores, in the secondstorage region 36B of the memory 36, the temperature Tm1, the humidityH1, the tension Tn1, and the width W1 received from therecording/reproduction apparatus 50A via the antenna coil 31. Inresponse to a request from the recording/reproduction apparatus 50A, thecontroller 35 of the cartridge memory 11 reads the temperature Tm1, thehumidity H1, the tension Tn1, and the width W1 from the memory 36 andtransmits them to the recording/reproduction apparatus 50A via theantenna coil 31.

[Operation of Recording/Reproduction Apparatus During Data Recording]

Hereinafter, an example of the operation of the recording/reproductionapparatus 50A during data recording will be described with reference toFIG. 16 .

First, the control device 59 loads the cartridge 10 into therecording/reproduction apparatus 50A (Step S101). Next, the controldevice 59 controls rotation of the spindle 51 and the reel 52, andcauses the magnetic tape MT to travel while applying specified tensionin the longitudinal direction of the magnetic tape MT. Then, the controldevice 59 records data on the magnetic tape MT by the magnetic head 56(Step S102).

Next, the control device 59 acquires, from the thermometer 63 and thehygrometer 64, the temperature Tm1 and the humidity H1 (environmentalinformation) around the magnetic tape MT during data recording (StepS103).

Next, the control device 59 calculates, on the basis of drive data ofthe spindle 51 and the reel 52 during data recording, the tension Tn1that has been applied in the longitudinal direction of the magnetic tapeMT during data recording (Step S104).

Next, the control device 59 obtains, on the basis of the reproductionwaveform of the servo signal read by the servo lead heads 56A and 56B ofthe magnetic head 56, the distance d1 between the two adjacent servobands SB. Next, the control device 59 calculates, on the basis of thedistance d1, the width W1 of the magnetic tape MT during data recording(Step S105).

Next, the control device 59 writes, by the reader/writer 57, thetemperature Tm1, the humidity H1, the tension Tn1, and the width W1 ofthe magnetic tape MT to the cartridge memory 11 as the informationduring data recording (Step S106).

[Operation of Recording/Reproduction Apparatus During Data Reproduction]

Hereinafter, an example of the operation of the recording/reproductionapparatus 50A during data reproduction will be described with referenceto FIG. 17 .

First, the control device 59 loads the cartridge 10 into therecording/reproduction apparatus 50A (Step S111). Next, the controldevice 59 reads, from the cartridge memory 11 by the reader/writer 57,the information during data recording (the temperature Tm1, the humidityH1, the tension Tn1, and the width W1 of the magnetic tape MT) writtento the cartridge memory 11 to acquire the information (Step S112). Next,the control device 59 acquires, by the thermometer 63 and the hygrometer64, information regarding the temperature Tm2 and information regardingthe humidity H2 around the present magnetic tape MT during datareproduction (Step S113).

Next, the control device 59 calculates a temperature difference TmD(TmD=Tm2−Tm1) between the temperature Tm1 during data recording and thetemperature Tm2 during data reproduction (Step S114). Further, thecontrol device 59 calculates the humidity difference HD (HD=H2−H1)between the humidity H1 during data recording and the humidity H2 duringdata reproduction (Step S115).

Next, the control device 59 multiplies the temperature difference TmD bya coefficient α (TmD×α), and multiplies the humidity difference HD by acoefficient β (HD×β) (Step S116). The coefficient α is a valueindicating how much the tension of the magnetic tape MT should bechanged per temperature difference of 1° C. compared to the tension Tn1during data recording. The coefficient β is a value indicating how muchthe tension of the magnetic tape MT should be changed per humiditydifference of 1% compared to the tension Tn1 during data recording.

Next, the control device 59 calculates the tension Tn2 to be applied inthe longitudinal direction of the magnetic tape MT during datareproduction (at present) by adding the value of TmD×α and the value ofHD×β to the tension Tn1 during data recording (Step S117).Tn2=Tn1+TmD×α+HD×β

After determining the tension Tn2 of the magnetic tape MT during datareproduction, the control device 59 controls rotation of the spindle 51and the reel 52 to control travelling of the magnetic tape MT so thatthe magnetic tape MT travels with the tension Tn2. Then, the controldevice 59 reproduces, by the data write/read head of the magnetic head56, the data recorded in the data track Tk while reading the servosignal of the servo band SB by the servo lead heads 56A and 56B of themagnetic head 56 (Step S118).

At this time, since the width of the magnetic tape MT has been adjustedto the width during data recording by adjusting the tension of themagnetic tape MT, the data write/read heads of the magnetic head 56 canbe accurately aligned to the data tracks Tk. As a result, even if thewidth of the magnetic tape MT fluctuates for some reason (e.g.,temperature and humidity fluctuations), it is possible to accuratelyreproduce data recorded on the magnetic tape MT.

Note that the value of the tension Tn2 to be applied to the magnetictape MT during data reproduction (at present) is higher if thetemperature during data reproduction is higher than the temperatureduring data recording. For this reason, in the case where thetemperature increase and the width of the magnetic tape MT is largerthan that during data recording, the width of the magnetic tape MT canbe narrowed to reproduce the same width as that during datareproduction.

On the contrary, the value of the tension Tn2 to be applied to themagnetic tape MT during data reproduction (at present) is lower if thetemperature during data reproduction is lower than the temperatureduring data recording. For this reason, in the case where thetemperature decrease and the width of the magnetic tape MT is smallerthan that during data recording, the width of the magnetic tape MT canbe widened to reproduce the same width as that during data reproduction.

Further, the value of the tension Tn2 to be applied to the magnetic tapeMT during data reproduction (at present) is higher if the humidityduring data reproduction is higher than the humidity during datarecording. For this reason, in the case where the humidity increase andthe width of the magnetic tape MT is larger than that during datarecording, the width of the magnetic tape MT can be narrowed toreproduce the same width as that during data reproduction.

On the contrary, the value of the tension Tn2 to be applied to themagnetic tape MT during data reproduction (at present) is lower if thehumidity during data reproduction is lower than the humidity during datarecording. For this reason, in the case where the humidity decrease andthe width of the magnetic tape MT is smaller than that during datarecording, the width of the magnetic tape MT can be widened to reproducethe same width as that during data reproduction.

Here, during data reproduction, in order to obtain the tension Tn2 to beapplied to the magnetic tape MT, information regarding the width W1 ofthe magnetic tape MT during data recording may further be used inaddition to the temperature Tm1, the humidity H1, and the tension Tn1 ofthe magnetic tape MT during data recording (or instead of the tensionTn1).

Also in this case, similarly, the control device 59 calculates thetemperature difference TmD (TmD=Tm2−Tm1) and the humidity difference HD(HD=H2−H1). Then, the control device 59 multiplies the temperaturedifference TmD by a coefficient γ (TmD×γ), and multiplies the humiditydifference HD by a coefficient δ (HD×δ) (Step S116).

Here, the coefficient γ is a value indicating how much the width of themagnetic tape MT fluctuates per temperature difference of 1° C. (valueindicating an expansion rate per unit length (in the width direction)based on the temperature). Further, the coefficient δ is a valueindicating how much the width of the magnetic tape MT fluctuates perhumidity difference of 1% (value indicating an expansion rate per unitlength (in the width direction) based on the humidity).

Next, the control device 59 predicts, on the basis of the width W1 ofthe magnetic tape MT in the past during data recording, the width W2 ofthe present magnetic tape MT during data reproduction by the followingformula.W2=W1(1+TmD×γ+HD2×δ)

Next, the control device 59 calculates a difference WD(WD=W2−W1=W1(TmD×γ+HD2×δ)) between the width W2 of the present magnetictape MT during data reproduction and the width W1 of the magnetic tapeMT in the past during data recording.

Then, the control device 59 adds the value obtained by multiplying thewidth difference WD by a coefficient E to the tension Tn1 of themagnetic tape MT during data recording to calculate the tension Tn2 ofthe magnetic tape MT during data reproduction.Tn2=Tn1+WD×ε

Here, the coefficient E is a value representing the tension in in thelongitudinal direction of the magnetic tape MT necessary for changingthe width of the magnetic tape MT by a unit distance.

After determining the tension Tn2 of the magnetic tape MT during datareproduction, the control device 59 controls rotation of the spindle 51and the reel 52, and controls travelling of the magnetic tape MT so thatthe magnetic tape MT travels with the tension Tn2. Then, the controldevice 59 reproduces, by the data write/read head of the magnetic head56, data recorded in the data track Tk while reading, by the servo leadheads 56A and 56B of the magnetic head 56, the servo signal of the servoband SB.

Also in the case where the tension Tn2 has been determined by such amethod, it is possible to accurately reproduce data recorded on themagnetic tape MT even when the width of the magnetic tape MT fluctuatesfor some reason (e.g., temperature and humidity fluctuations).

[Effect]

In the second embodiment, since the information during data recording ofthe magnetic tape MT is stored in the cartridge memory 11 as describedabove, it is possible to appropriately adjust the width of the magnetictape MT by using this information during data reproduction. Therefore,even if the width of the magnetic tape MT fluctuates for some reason, itis possible to accurately reproduce the data recorded on the magnetictape MT.

Further, in this embodiment, as the information during data recording,the temperature Tm1 and the humidity H1 (environmental information)around the magnetic tape MT during data recording is written. Therefore,it is possible to appropriately cope with fluctuations in the width ofthe magnetic tape MT and the width of the data track Tk due totemperature and humidity fluctuations.

3 Modified Example Modified Example 1

Although the case where the tension adjustment information is stored inthe cartridge memory 11 has been described in the above-mentioned firstand second embodiments, the tension adjustment information may be storedin the control device 59 of the recording/reproduction apparatus 50/50A.In this case, the control device 59 controls rotation of the spindledrive device 53 and the reel drive device 54 using the tensionadjustment information stored in the control device 59 to adjust thetension to be applied in the longitudinal direction of the magnetic tapeMT.

Modified Example 2

The magnetic tape MT may be used in a library apparatus. In this case,the library apparatus may have a configuration capable of adjusting thetension to be applied in the longitudinal direction of the magnetic tapeMT, and include a plurality of recording/reproduction apparatuses 50according to the first embodiment or a plurality ofrecording/reproduction apparatuses 50A according to the secondembodiment.

Modified Example 3

The servo writer may adjust the tension in the longitudinal direction ofthe magnetic tape MT during recording of the servo signal or the like tokeep the width of the magnetic tape MT constant or substantiallyconstant. In this case, the servo writer may include a detection devicethat detects the width of the magnetic tape MT, and adjust the tensionin the longitudinal direction of the magnetic tape MT on the basis ofthe detection result of the detection device.

Modified Example 4

The magnetic tape MT is not limited to a perpendicular recording typemagnetic tape, and may be a horizontal recording type magnetic tape. Inthis case, as the magnetic powder, a magnetic powder having a needleshape such as a metal magnetic powder may be used.

Modified Example 5

Although the case where the distance between servo bands SB is used asthe width-related information relating to the magnetic tape during datarecording has been described in the above-mentioned first embodiment,the width of the magnetic tape MT may be used.

In this case, the control device 59 calculates, during data recording,the width W1 of the magnetic tape MT from the distance d1 between theservo bands SB, and writes the width W1 to the cartridge memory 11 bythe reader/writer 57.

During data reproduction, the control device 59 reads, from thecartridge memory 11, the width W1 of the magnetic tape MT during datarecording, and calculates, on the basis of the distance d2 between theservo bands SB during data reproduction, the width W2 of the magnetictape MT during data reproduction. Then, the control device 59 calculatesthe difference ΔW between the width W1 of the magnetic tape MT duringdata recording and the width W2 of the magnetic tape MT during datareproduction, and determines whether or not the difference ΔW is withina specified value.

In the case where the difference Δd is within the specified value, thecontrol device 59 controls rotation driving of the spindle 51 and thereel 52 so that the specified tension is maintained. Meanwhile, in thecase where the difference Δd is not within the specified value, thecontrol device 59 controls rotation driving of the spindle 51 and thereel 52 so that the difference Δd is within the specified value toadjust the tension to be applied to the travelling magnetic tape MT.

Modified Example 6

Although the case where all of the temperatures Tm1 and Tm2, thehumidities H1 and H2, the tensions Tn1 and Tn2, and the widths W1 and W2are used as information during data recording has been described in theabove-mentioned second embodiment, the information during data recordingmay be any of the temperatures Tm1 and Tm2, the humidities H1 and H2,the tensions Tn1 and Tn2, and the widths W1 and W2 or any combination oftwo or three of them.

Not only information during data recording (the temperature Tm1, thehumidity H1, the tension Tn1, and the width W1) but also informationduring data reproduction (the temperature Tm2, the humidity H2, thetension Tn2, and the width W2) may be stored in the cartridge memory 11.For example, the information during data reproduction is used when datain the magnetic tape MT is reproduced and then the data is reproduced onanother occasion.

Modified Example 7

Although the case where the holes 43A are formed on the surface of themagnetic layer 43 by transferring the protrusions 44A provided on thesurface of the back layer 44 to the surface of the magnetic layer 43 hasbeen described in the above-mentioned first and second embodiments, themethod of forming the holes 43A is not limited thereto. For example, theholes 43A may be formed on the surface of the magnetic layer 43 byadjusting the type of the solvent contained in the coating material forforming a magnetic layer, the dry conditions of the coating material forforming a magnetic layer, and the like.

Example

Hereinafter, the present disclosure will be specifically described byway of Examples. However, the present disclosure is not limited to onlythese Examples.

In the following Examples and Comparative Examples, the averagethickness of a magnetic tape, the arithmetic average roughness Ra on thesurface of a magnetic layer, the squareness ratio in the verticaldirection, the average thickness of the magnetic layer, the BET specificsurface area, the pore distribution (pore diameter of the maximum porevolume at the time of attachment/detachment)), and the statistical valueσ_(SW) indicating the non-linearity of a servo pattern indicate valuesobtained by the measurement methods described in the above-mentionedfirst embodiment.

Example 1

(Process of Preparing Coating Material for Forming Magnetic Layer)

A coating material for forming a magnetic layer was prepared as follows.First, a first composition having the following formulation was kneadedby an extruder. Next, the kneaded first composition and a secondcomposition having the following formulation were added to a stirringtank including a dispersing device, and, premixed. Subsequently, furthersand mill mixing was performed, and filter treatment was performed toprepare a coating material for forming a magnetic layer.

(First Composition)

Powder (hexagon plate shape, the average aspect ratio of 2.8, and theaverage particle volume of 1600 nm³) of barium ferrite (BaFe₁₂O₁₉)particles: 100 parts by mass Vinyl chloride resin (resin solution: resincontent of 30 mass % and cyclohexanone of 70 mass %): 42 parts by mass(containing a solvent)

(Degree of polymerization 300, Mn=10000, containing OSO₃K=0.07 mmol/gand secondary OH=0.3 mmol/g as polar groups)

Aluminum oxide powder: 5 parts by mass

(α-Al₂O₃, average particle size of 0.1 μm)

Carbon black: 2 parts by mass

(Manufactured by TOKAI CARBON CO., LTD., trade name: SEAST TA)

(Second Composition)

Vinyl chloride resin: 3 parts by mass (containing a solvent)

(Resin solution: resin content of 30 mass % and cyclohexanone of 70 mass%)

n-butyl stearate: 2 parts by mass

Methyl ethyl ketone: 121.3 parts by mass

Toluene: 121.3 parts by mass

Cyclohexanone: 60.7 parts by mass

Finally, polyisocyanate (trade name: Coronate L manufactured by TOSOHCORPORATION): 4 parts by mass and myristic acid: 2 parts by mass wererespectively added as a curing agent and a lubricant to the coatingmaterial for forming a magnetic layer prepared as described above.

(Process of Preparing Coating Material for Forming Underlayer)

The coating material for forming an underlayer was prepared as follows.First, a third composition having the following formulation was kneadedby an extruder. Next, the kneaded third composition and a fourthcomposition having the following formulation were added to a stirringtank including a dispersing device, and premixed. Subsequently, furthersand mill mixing was performed, and filter treatment was performed toprepare a coating material for forming an underlayer.

(Third Composition)

Iron oxide powder having a needle shape: 100 parts by mass

(α-Fe₂O₃, the average major axis length of 0.15 μm)

Vinyl chloride resin: 60.6 parts by mass (containing a solvent)

(Resin solution: resin content of 30 mass % and cyclohexanone of 70 mass%)

Carbon black: 10 parts by mass

(Average particle size of 20 nm)

(Fourth Composition)

Polyurethane resin UR8200 (manufactured by TOYOBO CO., LTD.): 18.5 partsby mass

n-butyl stearate: 2 parts by mass

Methyl ethyl ketone: 108.2 parts by mass

Toluene: 108.2 parts by mass

Cyclohexanone: 18.5 parts by mass

Finally, polyisocyanate (trade name: Coronate L manufactured by TOSOHCORPORATION): 4 parts by mass and myristic acid: 2 parts by mass wererespectively added as a curing agent and a lubricant to the coatingmaterial for forming an underlayer prepared as described above.

(Process of Preparing Coating Material for Forming Back Layer)

A coating material for forming a back layer was prepared as follows. Thefollowing raw materials were mixed in a stirring tank including adispersing device, and filter treatment was performed to prepare acoating material for forming a back layer.

Powder of carbon black having a small particle size (average particlesize (D50) of 20 nm): 90 parts by mass

Powder of carbon black having a large particle size (average particlesize (D50) of 270 nm): 10 parts by mass

Polyester polyurethane: 100 parts by mass

(Manufactured by TOSOH CORPORATION, trade name: N-2304)

Methyl ethyl ketone: 500 parts by mass

Toluene: 400 parts by mass

Cyclohexanone: 100 parts by mass

(Coating Process)

The coating material for forming a magnetic layer and the coatingmaterial for forming an underlayer prepared as described above were usedto form an underlayer and a magnetic layer on one main surface of anelongated polyethylene naphthalate film (hereinafter, referred to as“PEN film”) having the average thickness of 4.2 μm, which was anon-magnetic support. First, the coating material for forming anunderlayer was coated on one main surface of the PEN film and dried toform an underlayer so that the average thickness after calendaring was0.9 μm. Next, the coating material for forming a magnetic layer wascoated on the underlayer and dried to form a magnetic layer so that theaverage thickness after calendaring was 80 nm. Note that during dryingof the coating material for forming a magnetic layer, the magnetic fieldof the magnetic powder was oriented in the thickness direction of thefilm by a solenoid coil. Further, the drying conditions (dryingtemperature and drying time) of the coating material for forming amagnetic layer were adjusted, and the squareness ratio S1 in thethickness direction (vertical direction) of the magnetic tape was set to65%. Subsequently, the coating material for forming a back layer wascoated on the other main surface of the PEN film and dried to form aback layer so that the average thickness after calendaring was 0.4 μm.In this way, a magnetic tape was obtained.

(Calendar Process and Transfer Process)

First, calendar processing was performed to smooth the surface of themagnetic layer. At this time, the conditions of the calendar processingwere adjusted and the arithmetic average roughness Ra on the surface ofthe magnetic layer was set to 2.5 nm. Next, after winding, into a roll,the obtained magnetic tape, first heat treatment of 60° C. was performedfor 10 hours on the magnetic tape in this state. Then, after re-windingthe magnetic tape into a roll so that the end portion located on theinner circumference side was located on the outer circumference side,second heat treatment of 60° C. was performed for 10 hours on themagnetic tape in this state. As a result, a large number of protrusionson the surface of the back layer were transferred to the surface of themagnetic layer, and a large number of holes were formed on the surfaceof the magnetic layer. The BET specific surface area of the entiremagnetic tape was 4.5 m²/g. Further, the average pore diameter of theentire magnetic tape MT was 8.0 nm.

(Cut Process)

The magnetic tape obtained as described above was cut into a width of ½inch (12.65 mm). As a result, an elongated magnetic tape having theaverage thickness of 5.6 μm was obtained.

(Process of Writing Servo Pattern)

A servo writer was used to write servo patterns to the magnetic tapeobtained as described above, and thus, five servo bands were formed. Theservo patterns conformed to the LTO-8 standard. As the servo writer, onehaving the configuration described in the first embodiment was used (seeFIG. 11 , Part A of FIG. 12 , and Part B of FIG. 12 ).

By adjusting the distance between a servo signal writing head and aguide roller and the angle of the tape entering the servo signal writinghead, the friction coefficient between the servo signal writing head andthe magnetic tape when recording the servo patterns was adjusted. As aresult, σ_(SW) of the magnetic tape was adjusted to 23 nm. In this way,the magnetic tape to which the servo patterns were written was obtained.

Example 2

A magnetic tape having the average thickness of 5.6 μm to which servopatterns were written was obtained in a similar way to Example 1 exceptthat the average thickness of the PEN film was 4.0 μm and the averagethickness of the underlayer was 0.6 μm in the coating process.

Example 3

A magnetic tape to which servo patterns were written was obtained in asimilar way to Example 1 except that the conditions of calendarprocessing were adjusted and the arithmetic average roughness Ra on thesurface of the magnetic layer was set to 2.2 nm in the calendar process.

Example 4

A magnetic tape to which servo patterns were written was obtained in asimilar way to Example 1 except that the drying conditions (dryingtemperature and drying time) of the coating material for forming amagnetic layer were adjusted and the squareness ratio of the magnetictape in the thickness direction (vertical direction) was set to 70%.

Example 5

A magnetic tape having the average thickness of 5.6 μm to which servopatterns were written was obtained in a similar way to Example 1 exceptthat the average thickness of the PEN film was 4.2 μm, the averagethickness of the underlayer after calendaring was 0.9 μm, and theaverage thickness of the magnetic layer after calendaring was 70 nm inthe coating process.

Example 6

A magnetic tape having the average thickness of 5.6 μm to which servopatterns were written was obtained in a similar way to Example 1 exceptthat the average thickness of the PEN film was 4.2 μm, the averagethickness of the underlayer after calendaring was 0.9 μm, and theaverage thickness of the magnetic layer after calendaring was 50 nm inthe coating process.

Example 7

A magnetic tape to which servo patterns were written was obtained in asimilar way to Example 1 except that the BET specific surface area wasset to 3.5 m²/g by setting the temperature of the first heat treatmentand the second heat treatment to 55° C. and the time of the first heattreatment and the second heat treatment to 10 hours in the transferprocess.

Example 8

A magnetic tape to which servo patterns were written was obtained in asimilar way to Example 1 except that the BET specific surface area wasset to 7.0 m²/g and the average pore diameter was set to 6.0 nm bysetting the temperature of the first heat treatment and the second heattreatment to 70° C. and the time of the first heat treatment and thesecond heat treatment to 10 hours in the transfer process.

Example 9

A magnetic tape to which servo patterns were written was obtained in asimilar way to Example 1 except that the statistical value σ_(SW)indicating the non-linearity of the servo pattern was set to 20 nm byreducing the friction coefficient between the servo signal writing headand the magnetic tape as compared with that in Example 1 in the processof writing the servo pattern.

Example 10

A magnetic tape to which servo patterns were written was obtained in asimilar way to Example 1 except that the statistical value σ_(SW)indicating the non-linearity of the servo pattern was set to 15 nm byreducing the friction coefficient between the servo signal writing headand the magnetic tape as compared with that in Example 9 in the processof writing the servo pattern.

Example 11

A magnetic tape to which servo patterns were written was obtained in asimilar way to Example 1 except that a powder of strontium ferriteparticles (having a hexagon plate shape, the aspect ratio of 2.9, andthe particle volume of 1600 nm³) was used as a magnetic powder in theprocess of forming a coating material for forming a magnetic layer.

Example 12

A magnetic tape to which servo patterns were written was obtained in asimilar way to Example 1 except that a powder of ε-iron oxide particles(having a spherical shape, the aspect ratio of 1.1, and the particlevolume of 1800 nm³) was used as a magnetic powder in the process offorming a coating material for forming a magnetic layer.

Example 13

A magnetic tape to which servo patterns were written was obtained in asimilar way to Example 1 except that a powder of cobalt ferrite (havinga cubic shape, the aspect ratio of 1.7, and the particle volume of 2000nm³) was used as a magnetic powder in the process of forming a coatingmaterial for forming a magnetic layer.

Example 14

A magnetic tape to which servo patterns were written was obtained in away similar to Example 3 except that the squareness ratio of themagnetic tape in the thickness direction (vertical direction) was set to70% by adjusting the drying conditions (drying temperature and dryingtime) of the coating material for forming a magnetic layer, and the BETspecific surface area was set to 3.5 m²/g and the average pore diameterwas set to 8.0 nm by setting the temperature of the first heat treatmentand the second heat treatment to 55° C. and the time of the first heattreatment and the second heat treatment to 10 hours in the transferprocess.

Example 15

A magnetic tape to which servo patterns were written was obtained in away similar to Example 14 except that the BET specific surface area wasset to 7.0 m²/g and the average pore diameter was set to 6.0 nm bysetting the temperature of the first heat treatment and the second heattreatment to 70° C. and the time of the first heat treatment and thesecond heat treatment to 10 hours in the transfer process.

Comparative Example 1

A magnetic tape to which servo patterns were written was obtained in asimilar way to Example 1 except that the statistical value σ_(SW)indicating the non-linearity of the servo pattern was set to 25 nm byincreasing the tension of the magnetic tape compared to that in Example1 and increasing the friction coefficient between the servo signalwriting head and the magnetic tape in the process of writing a servopattern.

Comparative Example 2

A magnetic tape to which servo patterns were written was obtained in asimilar way to Example 1 except that the arithmetic average roughness Raon the surface of the magnetic lager was set to 3.0 nm by adjusting theconditions of the calendar processing in the calendar processing.

Comparative Example 3

A magnetic tape to which servo patterns were written was obtained in asimilar way to Example 1 except that the squareness ratio of themagnetic tape in the thickness direction (vertical direction) was set to60% by adjusting the drying conditions (drying temperature and dryingtime) of the coating material for forming a magnetic layer.

Comparative Example 4

A magnetic tape having the average thickness of 5.6 μm to which servopatterns were written was obtained in a similar way to Example 1 exceptthat the average thickness of the PEN film was 4.2 μm, the averagethickness of the underlayer after calendaring was 0.9 μm, and theaverage thickness of the magnetic layer after calendaring was 90 nm inthe coating process.

Comparative Example 5

A magnetic tape to which servo patterns were written was obtained in asimilar way to Example 1 except that the BET specific surface area wasset to 3.2 m²/g and the average pore diameter was set to 9.0 nm bysetting the temperature of the first heat treatment and the second heattreatment to 55° C. and the time of the first heat treatment and thesecond heat treatment to 10 hours in the transfer process.

Comparative Example 6

A magnetic tape to which servo patterns were written was obtained in asimilar way to Example 1 except that the BET specific surface area wasset to 8.0 m²/g and the average pore diameter was set to 6.0 nm bysetting the temperature of the first heat treatment and the second heattreatment to 70° C. and the time of the first heat treatment and thesecond heat treatment to 20 hours in the transfer process.

[Evaluation]

(SNR)

The SNR of each of the magnetic tapes (magnetic tapes to which servopatterns had been written) according to Examples 1 to 15 and ComparativeExamples 1 to 6 was evaluated as follows. The SNR (electromagneticconversion characteristics) of the magnetic tape in the 25° C.environment was measured using a ½ inch tape travelling device(manufactured by Mountain Engineering II, INC., MTS Transport) to whicha recording/reproduction head and a recording/reproduction amplifier wasattached. A ring head having a gap length of 0.2 μm was used as therecording head, and a GMR head having a shield-to-shield distance of 0.1μm was used as the reproduction head. The relative speed was 6 m/s, therecording clock frequency was 160 MHz, and the recording track width was2.0 μm. Further, the SNR was calculated on the basis of the methoddescribed in the following literature. The results were shown in Table 2with the SNR in Example 1 as 0 dB.

Y. Okazaki: “An Error Rate Emulation System.”, IEEE Trans. Man., 31, pp.3093-3095(1995)

(Friction Coefficient Ratio)

The friction coefficient ratio (μ_(B)/μ_(A)) and the frictioncoefficient ratio (μ_(C)(1000)/μ_(C)(5)) of each of the magnetic tapesaccording to Examples 1 to 15 and Comparative Examples 1 to 6 wereevaluated by the evaluation method described in the above-mentionedfirst embodiment.

(Travelling Stability (1))

The travelling stability of each of the magnetic tapes (magnetic tapesto which servo patterns had been written) according to Examples 1 to 15and Comparative Examples 1 to 6 was evaluated as follows. The magnetictape was incorporated into an LTO cartridge. A so-called full volumetest in which data was recorded on the entire surface of the magnetictape and reproduced using an LTO drive connected to a server and a PCvia SCSI and Fibre Channel was performed on the LTO cartridge. In thefull volume test, the data recording status was sequentially monitored,and information relating to a problem was recorded when the problemoccurred.

In the full volume test, so-called stop write in which a driveautomatically pauses recording when the travelling status of themagnetic tape is unstable is performed. If the stop write is performed,the data transfer rate decreases. Further, in the full volume test, ifthe travelling state of the magnetic tape becomes more unstable, thedrive automatically stops recording completely and enters a so-calledfail state.

The full volume test was repeatedly performed 5 times sequentially onthe magnetic tapes according to Examples 1 to 15 and ComparativeExamples 1 to 6, and a “relative value of the transfer rate of the fifthfull volume test” and “presence or absence of fail” were recorded. Therelative value of the transfer rate of the full volume test is a ratioof the average transfer rate per full volume test to the transfer rateof the drive used for evaluation in the case where the highestperformance of the drive has been delivered. The case where the highestperformance of the drive was delivered is taken as 100%. For example, inthe case where an LTO8 drive is used to be connected to a server viaFibre Channel and recording is performed in the LTO8 format, thetransfer rate of the LTO8 drive when the drive delivered the highestperformance is 350 MB/sec. The “presence or absence of fail” indicateswhether or not the drive has become the fail state as described above.

Each of the magnetic tapes was evaluated in accordance with thefour-level evaluation criteria shown in the following Table 2. As shownin Table 2, the level 4 means having the best travelling stability, andthe level 1 means having the worst travelling stability. For example, inthe case where all the relative values of the transfer rate of themagnetic tape in the five full volume tests was 95% or more and 100% orless and there is no fail, the magnetic tape is rated as level 4. Arating of the level 4 or 3 (i.e., the transfer rate of the magnetic tapein the fifth full volume test is 80% or more) is desirable from theviewpoint of favorable travelling stability of the magnetic tape.

The evaluation result of each of the magnetic tapes is shown in thecolumn of “Travelling stability (1)”.

Table 2 shows details of the above-mentioned four-level determinationcriteria for travelling stability.

TABLE 2 Relative value of transfer rate Presence or of fifth full volumetest absence of fail Level 4 95% or more and 100% or less Absence Level3 80% or more and less than 95% Absence Level 2 Less than 80% AbsenceLevel 1 Less than 80% Presence

(Travelling Stability (2))

The travelling stability of each of the magnetic tapes (magnetic tapesto which servo patterns had been written) according to Examples 1 to 15and Comparative Examples 1 to 6 was evaluated as follows. First, as acartridge, one including a cartridge memory that includes, in a memory,a storage region to which tension adjustment information is written, andis capable of writing the tension adjustment information to theabove-mentioned region and reading the tension adjustment informationfrom the above-mentioned region by a controller was prepared. The sizeof this cartridge was similar to the size (102 mm×105 mm×22 mm) of thecartridge used for evaluation of the above-mentioned travellingstability (1).

Next, a full volume test was performed in a way similar to theabove-mentioned “travelling stability (1)” except that the tension inthe longitudinal direction of the magnetic tape was adjusted whenrecording and reproducing data on the entire surface of the magnetictape. Next, the travelling stability was evaluated in four levels, i.e.,levels 1 to 4, in a way similar to the above-mentioned “travellingstability (1)”.

The evaluation result of the travelling stability of each of themagnetic tapes is shown in the column of the “Travelling stability (2)”in Table 3.

The tension adjustment in the longitudinal direction of the magnetictape was performed as follows. That is, servo bands (servo tracks) intwo or more columns were reproduced at the same time while causing themagnetic tape to reciprocate by a recording/reproduction apparatus, andthe space between the servo pattern columns during travelling werecontinuously measured (for each point (specifically, for eachapproximately 6 mm) where there is information regarding the servoposition) on the basis of the shape of the reproduction waveform of eachof the servo pattern columns (servo signal) having an inverted V shapeof the servo bands. Then, the rotation driving of a spindle driveapparatus and a reel drive apparatus was controlled on the basis ofinformation regarding the measured space between the servo patterncolumns, and the tension in the longitudinal direction of the magnetictape was automatically adjusted so that the space between the servopattern columns approached a specified width. Here, the “specifiedwidth” means a distance between two servo read heads of therecording/reproduction apparatus. Note that the two servo read heads arelocated at positions of two servo bands located above and below the databand during travelling of the magnetic tape.

(Young's Modulus)

The Young's modulus of each of the magnetic tapes according to Examples1 to 15 and Comparative Examples 1 to 6 was measured by the method ofmeasuring the Young's modulus described in the above-mentioned firstembodiment.

Table 3 shows the configuration of each of the magnetic tapes accordingto Examples 1 to 15 and Comparative Examples 1 to 6, and the evaluationresults.

TABLE 3 Pore diameter of maxi- Mag- mum Trav- Trav- Arith- Square- neticpore elling elling Tape metic ness layer volume Friction sta- sta- aver-average ratio in aver- BET at time Statis- SNR Friction coef- bilitybility age rough- vertical age specific of attach- tical (Rela- coef-ficient (1) (2) thick- ness direc- thick- surface ment/ value tiveficient ratio (Ab- (Pres- Young's Magnetic Sub- ness Ra tion ness areadetach- σ_(SW) value) ratio μ_(C)(1000)/ sence ence modulus materialstrate [μm] [nm] [%] [nm] [m²/g] ment [nm] [dB] μ₀/μ_(A) μ_(C)(5) of TC)of TC) [GPa] Exam- BaFe₁₂O₁₉ PEN 5.6 2.5 65 80 4.5 8.0 23 0.0 1.2 1.2 33 7.8 ple 1 Exam- BaFe₁₂O₁₉ PEN 5.1 2.5 65 80 4.5 9.0 23 0.0 1.2 1.2 3 37.5 ple 2 Exam- BaFe₁₂O₁₉ PEN 5.6 2.2 65 80 4.5 8.0 23 0.3 1.2 1.3 3 37.8 ple 3 Exam- BaFe₁₂O₁₉ PEN 5.6 2.5 70 80 4.5 8.0 23 0.3 1.2 1.3 3 37.8 ple 4 Exam- BaFe₁₂O₁₉ PEN 5.6 2.5 65 70 4.5 8.0 23 0.4 1.2 1.2 3 37.8 ple 5 Exam- BaFe₁₂O₁₉ PEN 5.6 2.5 65 50 4.5 8.0 23 0.4 1.2 1.2 3 37.8 ple 6 Exam- BaFe₁₂O₁₉ PEN 5.6 2.5 65 80 3.5 8.0 23 0.0 1.2 1.4 3 37.8 ple 7 Exam- BaFe₁₂O₁₉ PEN 5.6 2.5 65 80 7.0 6.0 23 0.0 1.4 1.2 3 37.8 ple 8 Exam- BaFe₁₂O₁₉ PEN 5.6 2.5 65 80 4.5 8.0 20 0.0 1.2 1.2 4 47.8 ple 9 Exam- BaFe₁₂O₁₉ PEN 5.6 2.5 65 80 4.5 8.0 15 0.0 1.2 1.2 4 47.8 ple 10 Exam- BaFe₁₂O₁₉ PEN 5.6 2.5 65 80 4.5 8.0 23 0.0 1.2 1.2 3 37.8 ple 11 Exam- ε-iron PEN 5.6 2.5 65 80 4.5 10.0 23 0.1 1.2 1.2 3 37.8 ple 12 oxide Exam- Co-iron PEN 5.6 2.5 65 80 4.5 9.0 23 0.2 1.2 1.23 3 7.8 ple 13 oxide Exam- BaFe₁₂O₁₉ PEN 5.6 2.2 70 80 3.5 8.0 23 0.41.5 1.9 3 3 7.8 ple 14 Exam- BaFe₁₂O₁₉ PEN 5.6 2.2 70 80 7.0 6.0 23 0.41.9 1.5 3 3 7.8 ple 15 Compar- BaFe₁₂O₁₉ PEN 5.6 2.5 65 80 4.5 8.0 250.0 1.2 1.2 2 2 7.8 ative Exam- ple 1 Compar- BaFe₁₂O₁₉ PEN 5.6 3.0 6580 4.5 8.0 23 −0.7 1.1 1.2 3 3 7.8 ative Exam- ple 2 Compar- BaFe₁₂O₁₉PEN 5.6 2.5 60 80 4.5 8.0 23 −0.7 1.2 1.2 3 3 7.8 ative Exam- ple 3Compar- BaFe₁₂O₁₉ PEN 5.6 2.5 65 90 4.5 8.0 23 −0.7 1.2 1.4 3 2 7.8ative Exam- ple 4 Compar- BaFe₁₂O₁₉ PEN 5.6 2.5 65 80 3.2 9.0 23 0.0 2.22.1 2 1 7.8 ative Exam- ple 5 Compar- BaFe₁₂O₁₉ PEN 5.6 2.5 65 80 8.06.0 23 0.0 2.2 2.3 2 1 7.8 ative Exam- ple 6 PEN: polyethylene TC:Tension control

The above-mentioned evaluation results show the following.

The travelling stability is reduced in the case where the BET specificsurface area of the entire magnetic tape measured in the state where themagnetic tape has been washed and dried is outside the range of 3.5 m²/gor more and 7.0 m²/g or less (Examples 1, 7, and 8, and ComparativeExamples 5 and 6).

The travelling stability is reduced in the case where the statisticalvalue σ_(SW) indicating the non-linearity of the servo pattern columns(servo bands) exceeds 24 nm (Examples 1, 9, and 10, and ComparativeExample 1).

The electromagnetic conversion characteristics (SNR) deteriorate in thecase where the arithmetic average roughness Ra on the surface of themagnetic layer exceeds 2.5 nm (Examples 1 and 3, and Comparative Example2).

The electromagnetic conversion characteristics (SNR) deteriorate in thecase where the squareness ratio of the magnetic layer in the verticaldirection is less than 65% (Examples 1 and 4, and Comparative Example3).

The electromagnetic conversion characteristics (SNR) deteriorate in thecase where the average thickness of the magnetic layer exceeds 80 nm(Examples 1, 5, and 6, and Comparative Example 4).

Therefore, in order to achieve both excellent travelling stability andexcellent electromagnetic conversion characteristics in the magnetictape having the average thickness of 5.6 μm or less, the BET specificsurface area of the entire magnetic tape is 3.5 m²/g or more and 7.0m²/g or less, the statistical value σ_(SW) indicating the non-linearityof the servo pattern is 24 nm or less, the arithmetic average roughnessRa of the surface of the magnetic layer is 2.5 nm or less, thesquareness ratio of the magnetic layer in the vertical direction is 65%or more, and the average thickness of the magnetic layer is 80 nm orless.

Even in the case where a powder of strontium ferrite particles is usedinstead of a powder of barium ferrite particles as a magnetic powder, itis possible to achieve both excellent travelling stability and excellentelectromagnetic conversion characteristics in the magnetic tape havingthe average thickness of 5.6 μm or less by causing the BET specificsurface area, the statistical value σ_(SW), the arithmetic averageroughness Ra, the squareness ratio, and the average thickness of themagnetic layer to satisfy the above-mentioned numerical value range(Examples 1 and 11).

Even in the case where a powder of ε-iron oxide particles or a powder ofcobalt ferrite particles is used instead of hexagonal ferrite particles(a powder of barium ferrite particles, a powder of strontium ferriteparticles) as a magnetic powder, it is possible to achieve bothexcellent travelling stability and excellent electromagnetic conversioncharacteristics in the magnetic tape having the average thickness of 5.6μm or less by causing the BET specific surface area, the statisticalvalue σ_(SW), the arithmetic average roughness Ra, the squareness ratio,and the average thickness of the magnetic layer to satisfy theabove-mentioned numerical value range (Examples 1, 12, and 13).

Even in the case where the tension of the magnetic tape is adjusted, itis possible to achieve both excellent travelling stability and excellentelectromagnetic conversion characteristics in the magnetic tape havingthe average thickness of 5.6 μm or less by causing the BET specificsurface area, the statistical value σ_(SW), the arithmetic averageroughness Ra, the squareness ratio, and the average thickness of themagnetic layer to satisfy the above-mentioned numerical value range(Example 1).

In order to achieve more excellent travelling stability in the magnetictape having the average thickness of 5.6 μm or less, it is favorablethat the statistical value σ_(SW) indicating the non-linearity of theservo pattern columns (servo bands) is 20 nm or less (Examples 1, 9, and10).

In order to achieve more excellent electromagnetic conversioncharacteristics, it is favorable that the arithmetic average roughnessRa on the surface of the magnetic layer is 2.2 nm or less (Examples 1and 3).

In order to achieve more excellent electromagnetic conversioncharacteristics, it is favorable that the squareness ratio of themagnetic layer in the vertical direction is 70% or more (Examples 1 and4).

In the case where the friction coefficient ratio (μ_(B)/μ_(A)) is withinthe range of 1.0 or more and 2.0 or less, excellent travelling stabilitycan be achieved even if the tension of the magnetic tape having theaverage thickness of 5.6 μm or less is controlled (Examples 1, 8, 14,and 15, and Comparative Examples 5 and 6).

In the case where the friction coefficient ratio is(μ_(C)(1000)/μ_(C)(5) is within the range of 1.0 or more and 2.0 orless, excellent travelling stability can be achieved even afterperforming the five full volume tests on the magnetic tape having theaverage thickness of 5.6 μm or less (i.e., even after causing themagnetic tape having the average thickness of 5.6 μm or less to travelmore than 1000 times) (Examples 1, 3, 7, 14, and 15, and ComparativeExamples 5 and 6).

Although embodiments of the present disclosure and modified examplesthereof have been specifically described above, the present disclosureis not limited to the above-mentioned embodiments and modified examplesthereof and various modifications can be made on the basis of thetechnical idea of the present disclosure. For example, theconfigurations, the methods, the processes, the shapes, the materials,and the numerical values cited in the above-mentioned embodiments andmodified examples thereof are only illustrative, and differentconfigurations, methods, processes, shapes, materials, and numericalvalues may be used as necessary. The configurations, the methods, theprocesses, the shapes, the materials, and the numerical values of theabove-mentioned embodiments and modified examples thereof can becombined with each other without departing from the essence of thepresent disclosure.

The chemical formulae of the compounds illustrated in theabove-mentioned embodiments and modified examples thereof arerepresentative, and are not limited to the listed valances or the likeas long as they have the general name of the same compound. Within thenumerical range described in a stepwise manner in the above-mentionedembodiments and modified examples thereof, the upper limit value or thelower limit value of the numerical range in a certain step may bereplaced with the upper limit value or the lower limit value of thenumerical range in another step. The materials illustrated in theabove-mentioned embodiments and modified examples thereof can be usedalone or in combination unless otherwise specified.

Further, the present disclosure may also take the followingconfigurations.

(1)

A tape-shaped magnetic recording medium, including:

a substrate;

an underlayer provided on the substrate; and

a magnetic layer provided on the underlayer, wherein

the substrate contains polyester,

each of the underlayer and the magnetic layer contains a lubricant,

the magnetic layer has a surface on which a large number of holes isprovided,

the arithmetic average roughness Ra of the surface is 2.5 nm or less,

a BET specific surface area of the entire magnetic recording mediummeasured in a state where the magnetic recording medium has been washedand dried is 3.5 m²/g or more and 7.0 m²/g or less,

a squareness ratio of the magnetic layer in a vertical direction is 65%or more,

an average thickness of the magnetic layer is 80 nm or less,

an average thickness of the magnetic recording medium is 5.6 μm or less,and

a servo pattern is recorded on the magnetic layer and a statisticalvalue σ_(SW) indicating a non-linearity of the servo pattern is 24 nm orless.

(2)

The magnetic recording medium according to (1), in which

the statistical value σ_(SW) is 23 nm or less.

(3)

The magnetic recording medium according to (1), in which

the statistical value σ_(SW) is 20 nm or less.

(4)

The magnetic recording medium according to any one of (1) to (3), inwhich

the squareness ratio is 70% or more.

(5)

The magnetic recording medium according to any one of (1) to (4), inwhich

the arithmetic average roughness Ra is 2.2 nm or less.

(6)

The magnetic recording medium according to any one of (1) to (5), inwhich

a friction coefficient ratio (μ_(B)/μ_(A)) between a dynamic frictioncoefficient μ_(A) between the surface the magnetic layer and a magnetichead when tension applied to the magnetic recording medium is 1.2 N, anda dynamic friction coefficient μ_(B) between the surface of the magneticlayer and the magnetic head when tension applied to the magneticrecording medium is 0.4 N is 1.0 or more and 2.0 or less.

(7)

The magnetic recording medium according to any one of (1) to (6), inwhich

regarding the dynamic friction coefficient μ_(C) between the surface ofthe magnetic layer and a magnetic head when tension applied to themagnetic recording medium is 0.6 N, a friction coefficient ratio(μ_(C)(1000)/μ_(C)(5)) of a dynamic friction coefficient μ_(C)(1000) ofthe 1000th travelling to a dynamic friction coefficient μ_(C)(5) of thefifth travelling is 1.0 or more and 2.0 or less.

(8)

The magnetic recording medium according to any one of (1) to (7), inwhich

an average pore diameter of the entire magnetic recording mediummeasured in the state where the magnetic recording medium has beenwashed and dried is 6 nm or more and 11 nm or less.

(9)

The magnetic recording medium according to any one of (1) to (8), inwhich

a coercive force Hc of the magnetic layer in a longitudinal direction is2000 Oe or less.

(10)

The magnetic recording medium according to any one of (1) to (9), inwhich

the magnetic layer includes 5 or more servo bands.

(11)

The magnetic recording medium according to (10), in which

a ratio of the total area of the servo bands to the area of the surfaceis 4.0% or less.

(12)

The magnetic recording medium according to (10) or (11), in which

a width of each of the servo bands is 95 μm or less.

(13)

The magnetic recording medium according to any one of (1) to (12), inwhich

the magnetic layer is configured to be capable of forming a plurality ofdata tracks, and

a width of each of the data tracks is 2000 nm or less.

(14)

The magnetic recording medium according to any one of (1) to (13), inwhich

the magnetic layer is configured to be capable of recording data so thatthe minimum value of a magnetization reversal pitch L is 48 nm or less.

(15)

The magnetic recording medium according to any one of (1) to (14), inwhich

the average thickness of the substrate is 4.2 μm or less.

(16)

The magnetic recording medium according to any one of (1) to (15), inwhich

the lubricant contains at least one type selected from a fatty acid anda fatty acid ester, and

the fatty acid contains a compound represented by the following generalformula (1) or (2), and the fatty acid ester contains a compoundrepresented by the following general formula (3) or (4).CH₃(CH₂)_(k)COOH  (1)

(wherein k is an integer selected from a range of 14 or more and 22 orless in the general formula (1).)CH₃(CH₂)_(n)CH═CH(CH₂)_(m)COOH  (2)

(wherein a sum of n and m is an integer selected from a range of 12 ormore and 20 or less in the general formula (2).)CH₃(CH₂)_(p)COO(CH₂)_(q)CH₃  (3)

(wherein p is an integer selected from a range of 14 or more and 22 orless and q is in integer selected from a range of 2 or more and 5 orless in the general formula (3).)CH₃(CH₂)_(r)COO—(CH₂)_(s)CH(CH₃)₂  (4)

(wherein r is an integer selected from a range of 14 or more and 22 orless and s is an integer selected from a range of 1 or more and 3 orless in the general formula (4).)

(17)

The magnetic recording medium according to any one of (1) to (16), inwhich

the magnetic layer contains a magnetic powder, and

the magnetic powder includes hexagonal ferrite, ε-iron oxide, orCo-containing spinel ferrite.

(18)

The magnetic recording medium according to (17), in which

the hexagonal ferrite contains at least one type of Ba or Sr, and

the ε-iron oxide contains at least one type of Al or Ga.

(19)

A cartridge, including:

the magnetic recording medium according to any one of (1) to (18); and

a storage unit that has a region to which adjustment information foradjusting tension to be applied in a longitudinal direction of themagnetic recording medium is written.

(20)

The cartridge according to (19), in which

a communication unit that communicates with a recording/reproductionapparatus; and

a control unit that

-   -   stores, in the region, the adjustment information received from        the recording/reproduction apparatus via the communication unit,        and    -   reads the adjustment information from the region and transmits        the adjustment information to the recording/reproduction        apparatus via the communication unit in response to a request        from the recording/reproduction apparatus.

REFERENCE SIGNS LIST

-   -   10 cartridge    -   11 cartridge memory    -   31 antenna coil    -   32 rectification/power circuit    -   33 clock circuit    -   34 detection/modulation circuit    -   35 controller    -   36 memory    -   36A first storage region    -   36B second storage region    -   41 substrate    -   42 underlayer    -   43 magnetic layer    -   44 back layer    -   50, 50A recording/reproduction apparatus    -   51 spindle 51    -   52 reel 52    -   53 spindle drive apparatus    -   54 reel drive apparatus    -   55 guide roller    -   56 magnetic head    -   57 reader/writer    -   58 communication interface    -   59 control apparatus    -   60 network    -   61 hygrometer 61    -   62 PC    -   63 thermometer    -   64 hygrometer    -   100, 100A recording/reproduction system    -   110 servo frame    -   111 servo subframe 1    -   111A A burst    -   111B B burst    -   112 servo subframe 2    -   112C C burst    -   112C C burst    -   113 servo stripe    -   MT magnetic tape    -   SB servo band    -   DB data band

The invention claimed is:
 1. A magnetic recording medium, comprising: asubstrate; an underlayer provided on the substrate; and a magnetic layerprovided on the underlayer, wherein the substrate contains polyester,each of the underlayer and the magnetic layer contains a lubricant, themagnetic layer has a surface on which a large number of holes isprovided, the arithmetic average roughness Ra of the surface is 2.5 nmor less, a BET specific surface area of the entire magnetic recordingmedium measured in a state where the magnetic recording medium has beenwashed and dried is 3.5 m²/g or more and 7.0 m²/g or less, a squarenessratio of the magnetic layer in a vertical direction is 65% or more, anaverage thickness of the magnetic layer is 80 nm or less, an averagethickness of the magnetic recording medium is 5.6 μm or less, and aservo pattern is recorded on the magnetic layer and a statistical valueσ_(sw) indicating a non-linearity of the servo pattern is 24 nm or less,wherein the statistical value σ_(sw) is defined by:σ_(SW)=√{square root over (ΣWIP(f)×df)}  (1) wherein WIP(f) is adisplacement difference during actual drive and df is a wave numberinterval, wherein regarding a dynamic friction coefficient μc betweenthe surface of the magnetic layer and a magnetic head when tensionapplied to the magnetic recording medium is 0.6 N, a frictioncoefficient ratio (μc(1000)/μc(5)) of a dynamic friction coefficientμc(1000) of a 1000th travelling to a dynamic friction coefficient μc(5)of a fifth travelling is 1.0 or more and 2.0 or less, and wherein themagnetic recording medium is tape-shaped.
 2. The magnetic recordingmedium according to claim 1, wherein the statistical value σ_(sw) is 23nm or less.
 3. The magnetic recording medium according to claim 1,wherein the statistical value σ_(sw) is 20 nm or less.
 4. The magneticrecording medium according to claim 1, wherein the squareness ratio is70% or more.
 5. The magnetic recording medium according to claim 1,wherein the arithmetic average roughness Ra is 2.2 nm or less.
 6. Themagnetic recording medium according to claim 1, wherein a frictioncoefficient ratio (μ_(B)/μ_(A)) between a dynamic friction coefficientμ_(A) between the surface the magnetic layer and a magnetic head whentension applied to the magnetic recording medium is 1.2 N, and a dynamicfriction coefficient μ_(B) between the surface of the magnetic layer andthe magnetic head when tension applied to the magnetic recording mediumis 0.4 N is 1.0 or more and 2.0 or less.
 7. The magnetic recordingmedium according to claim 1, wherein an average pore diameter of theentire magnetic recording medium measured in the state where themagnetic recording medium has been washed and dried is 6 nm or more and11 nm or less.
 8. The magnetic recording medium according to claim 1,wherein a coercive force Hc of the magnetic layer in a longitudinaldirection is 2000 Oe or less.
 9. The magnetic recording medium accordingto claim 1, wherein the magnetic layer includes 5 or more servo bands.10. The magnetic recording medium according to claim 9, wherein a ratioof the total area of the servo bands to the area of the surface is 4.0%or less.
 11. The magnetic recording medium according to claim 9, whereina width of each of the servo bands is 95 μm or less.
 12. The magneticrecording medium according to claim 1, wherein the magnetic layer isconfigured to be capable of forming a plurality of data tracks, and awidth of each of the data tracks is 2000 nm or less.
 13. The magneticrecording medium according to claim 1, wherein the magnetic layer isconfigured to be capable of recording data so that the minimum value ofa magnetization reversal pitch L is 48 nm or less.
 14. The magneticrecording medium according to claim 1, wherein the average thickness ofthe substrate is 4.2 μm or less.
 15. The magnetic recording mediumaccording to claim 1, wherein the lubricant contains at least one typeselected from a fatty acid and a fatty acid ester, and the fatty acidcontains a compound represented by the following general formula (1) or(2), and the fatty acid ester contains a compound represented by thefollowing general formula (3) or (4),CH₃(CH₂)_(k)COOH  (1) wherein k is an integer selected from a range of14 or more and 22 or less in the general formula (1),CH₃(CH₂)_(n)CH═CH(CH₂)_(m)COOH  (2) wherein a sum of n and m is aninteger selected from a range of 12 or more and 20 or less in thegeneral formula (2),CH₃(CH₂)_(p)COO(CH₂)_(q)CH₃  (3) wherein p is an integer selected from arange of 14 or more and 22 or less and q is in integer selected from arange of 2 or more and 5 or less in the general formula (3),CH₃(CH₂)_(r)COO—(CH₂)_(s)CH(CH₃)₂  (4) wherein r is an integer selectedfrom a range of 14 or more and 22 or less and s is an integer selectedfrom a range of 1 or more and 3 or less in the general formula (4). 16.The magnetic recording medium according to claim 1, wherein the magneticlayer contains a magnetic powder, and the magnetic powder includeshexagonal ferrite, ε-iron oxide, or Co-containing spinel ferrite. 17.The magnetic recording medium according to claim 16, wherein thehexagonal ferrite contains at least one type of Ba or Sr, and the ε-ironoxide contains at least one type of Al or Ga.
 18. A cartridge,comprising: the magnetic recording medium according to claim 1; and astorage unit that has a region to which adjustment information foradjusting tension to be applied in a longitudinal direction of themagnetic recording medium is written.
 19. The cartridge according toclaim 18, further comprising a communication unit that communicates witha recording/reproduction apparatus; and a control unit that stores theadjustment information received from the recording/reproductionapparatus via the communication unit, and reads the adjustmentinformation from the region and transmits the adjustment information tothe recording/reproduction apparatus via the communication unit inresponse to a request from the recording/reproduction apparatus.